The Journal of Infectious Diseases MAJOR ARTICLE
Natural Acquired Immunity Against Subsequent Genital Human Papillomavirus Infection: A Systematic Review and Meta-analysis Daniel C. Beachler, Gwendolyne Jenkins, Mahboobeh Safaeian, Aimée R. Kreimer, and Nicolas Wentzensen Division of Cancer Epidemiology, and Genetics, National Cancer Institute, Bethesda, Maryland
Background. Studies have been mixed on whether naturally acquired human papillomavirus (HPV) antibodies may protect against subsequent HPV infection. We performed a systematic review and meta-analysis to assess whether naturally acquired HPV antibodies protect against subsequent genital HPV infection (ie, natural immunity). Methods. We searched the MEDLINE and EMBASE databases for studies examining natural HPV immunity against subsequent genital type-specific HPV infection in female and male subjects. We used random-effects models to derive pooled relative risk (RR) estimates for each HPV type. Results. We identified 14 eligible studies that included >24 000 individuals from 18 countries that examined HPV natural immunity. We observed significant protection against subsequent infection in female subjects with HPV-16 ( pooled RR, 0.65; 95% confidence interval, .50–.80) and HPV-18 (0.70; .43–.98) but not in male subjects (HPV-16: 1.22; .67–1.77 [P = .05 (test for heterogeneity)]; HPV-18: 1.50; .46–2.55; [P = .15]). We also observed type-specific protection against subsequent infection for a combined measure of HPV-6/11/31/33/35/45/52/58 in female subjects ( pooled RR, 0.75; 95% confidence interval, .57–.92). Natural immunity was also evident in female subjects when analyses were restricted to studies that used neutralizing assays, used HPV persistence as an outcome, or reported adjusted analyses (each P < .05). Conclusions. HPV antibodies acquired through natural infection provide modest protection against subsequent cervical HPV infection in female subjects. Keywords. human papillomavirus; antibodies; serology; natural immunity; cervix.
The majority of sexually active individuals acquire ≥1 alphagenus human papillomavirus (HPV) genotype at their genital regions during their lifetime [1]. Although in most individuals the HPV infection can be cleared or controlled within 1 or 2 years [2, 3], HPV persists in the epithelium of a subset of infected individuals and can progress to cancer at several anatomic sites, particularly at the cervix [4]. At least some of the women whose HPV infection is cleared seem to lack lifelong immunity, because type-specific HPV infections can reappear among previously exposed individuals [5]. These HPV reappearances can occasionally progress at least to precancer [5, 6]. In approximately 60%–70% of women who acquire an HPV infection, a measurable type-specific serum antibody response against epitopes develops on the HPV L1 capsid protein [7, 8], representing an insensitive marker of cumulative HPV
Received 27 October 2015; accepted 14 December 2015; published online 21 December 2015. Correspondence: D. C. Beachler, Infections and Immunoepidemiology Branch, Division of Cancer Epidemiology and Genetics, National Cancer Institute, 9609 Medical Center Dr, RM 6-E220, Bethesda, MD 20892 ([email protected]). The Journal of Infectious Diseases® 2016;213:1444–54 Published by Oxford University Press for the Infectious Diseases Society of America 2015. This work is written by (a) US Government employee(s) and is in the public domain in the US. DOI: 10.1093/infdis/jiv753
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exposure [9]. Theoretically, these antibodies could help protect individuals from subsequent infections with that HPV type. Indeed, some have hypothesized that this “natural HPV immunity” may help partially explain the declining cervical HPV prevalence by age seen in some countries [10, 11] and that this immunity could be used as a factor in costeffectiveness models evaluating HPV vaccination of older populations [12]. Protection through naturally acquired polyclonal antibodies is plausible, given that the strong antibodies responses to prophylactic HPV vaccination are believed to be responsible for the protection observed among vaccinated individuals [13]. However, the antibody levels in vaccinated women are orders of magnitude higher than natural antibody levels. Previous study findings seem to be mixed on whether individuals with HPV antibodies acquired from natural HPV infection are protected against subsequent genital HPV infection [6, 11, 14–25]. These studies were often relatively small and used different populations, assays, and analytic techniques that may have affected the discordant results. Therefore we performed a systematic review and meta-analysis of this literature to determine more definitively whether naturally acquired HPV antibodies are protective against subsequent genital HPV infection in unvaccinated individuals.
METHODS Search Strategy and Selection Criteria
We systematically reviewed the biomedical literature for studies conducted between 1 January 1950 and 6 July 2015 using the MEDLINE and EMBASE databases. Key search terms included the following: “human papillomavirus” or “HPV” and “serology” or “viruslike particles” or “seropositivity.” Two of the authors (D. C. B. and G. J.) independently identified eligible publications by reviewing titles and abstracts, and also by searching the reference lists of eligible publications. When an abstract’s content was considered inadequate to determine inclusion, the full text of the article was reviewed. Studies included in the systematic review were required to be longitudinal and needed to evaluate “natural HPV immunity” by testing for HPV L1 serology. Studies must have compared the risk of subsequent genital HPV infection (DNA) among individuals who were HPV seropositive or HPV seronegative at the start of follow-up. We defined HPV natural immunity as HPV antibodies significantly protecting against a subsequent type-specific infection. We did not evaluate whether HPV antibodies protect against subsequent HPV-related types in the same clade (ie, HPV-16 antibodies against HPV-31/33/35/52/ 58 infection). We excluded any studies that did not restrict to individuals who were HPV DNA negative (for the homologous type of interest) at the entry of the analysis. We also restricted analysis to studies that examined genital HPV (DNA) infection as the outcome, because only 2 identifiable studies examined nongenital HPV infection as an outcome [20, 26]. Every other study examining natural immunity against genital HPV infection was included regardless of their study population, including those with human immunodeficiency virus (HIV)–infected individuals. Data Extraction
We extracted data from the included studies using a standardized data-collection form. We included analyses for any alphamucosal HPV genotype. Every included study examined HPV DNA (infection) status measured through polymerase chain reaction (PCR)–based methods with varying primers. Many studies reported multiple outcome results; for this meta-analysis, we used the longest detected infection-level measure (up to 12month persistence) for our main pooled analysis. For example, we used a 6-month persistent HPV infection instead of a onetime detection of HPV for the main pooled analysis when both were presented in an article. However, we also included both results in separate subanalyses specific for 6-month persistent infection and one-time detection. Seven separate publications used the same 3 longitudinal cohort populations. Our main pooled analysis included only 1 publication from each of the 3 populations, selecting the publication using the more sensitive serologic assay (highest percentage of HPV-seropositive individuals) and the largest sample
size, because we were most interested in determining the estimate of protection among all individuals with evidence of previous HPV exposure. Although no current serologic assay seems to be perfectly sensitive for HPV exposure, assays that measure a polyclonal response, such as the viruslike particle enzymelinked immunosorbent assay (VLP-ELISA), seem more sensitive than those that only measure epitope-specific neutralizing antibodies, such as the competitive Luminex Immunoassay (cLIA) [9, 24, 27]. However, in subanalyses examining assayspecific results we included estimates from 2 other publications [15, 24] that compared results using multiple serologic assays. Most studies defined their seropositivity thresholds as 3 or 5 standard deviations above the mean titer/optical density/ intensity level in concurrently tested specimens from virgins, after excluding positive outliers. Some studies presented multiple results using different seropositive cutoff estimates. We used the main cutoff in each article that was presented in the abstract and/or in tables. Data Analysis
Random effect meta-analysis techniques were used to generate pooled summary estimates for HPV-16 and HPV-18 [28]. These 2 HPV types are known to cause approximately 70% of cervical cancer and >80% of HPV-associated noncervical cancers [2, 29, 30]. Natural immunity against 8 alpha HPV types (types 6, 11, 31, 33, 35, 45, 52, and 58) was also each analyzed in a typespecific manner, but these results were then pooled, given that the analyses were restricted to 1–4 publications, depending on the type. A global pooled estimate of natural immunity against all tested HPV types was also calculated. We used adjusted analyses in the meta-analyses when they were available, and we conducted subgroup analysis to examine whether sex may be a source of heterogeneity. We also used the longest detectable HPV infection end point when available (12-month persistent infection in 1 study and 6-month persistent infection in 3). In addition, we performed 4 subgroup analyses, comparing (1) studies that used neutralizing serologic assays (eg, cLIA) with those that used neutralizing and nonneutralizing serologic assay (eg, VLP-ELISA); (2) studies that used MY09-MY11 consensus primer PCR with those that used the SPF10-DEIA PCR method for DNA detection; (3) studies that used a 6-month persistent HPV DNA end point with those that used one-time detection of HPV DNA as an end point; and (4) studies that reported adjusted analyses with those that reported only unadjusted analyses. We examined heterogeneity using the I 2 and χ2 statistics [31], and publication bias using funnel plots and Egger and Begg P values [32, 33], and we performed meta-analyses with Stata SE software (version 13.1; StataCorp) [34]. RESULTS
We systematically searched 1531 articles, and excluded 1490 because the study was not longitudinal, did not test for HPV Meta-analysis of HPV Natural Immunity
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DNA, or did not test for HPV serology. The full texts of each of the remaining 41 studies were reviewed, and 14 articles were identified to meet the inclusion criteria (Figure 1). The included studies spanned 18 countries and included >24 000 HPV unvaccinated individuals (Table 1). Most studies were restricted to female subjects, examining immunity against cervical HPV (11 of 14 publications, approximately 90% of total population) and the majority were conducted in the United States or Costa Rica (10 of 14 publications, approximately 55% of total population). More than half of the studies used the VLP-ELISA as their serologic assay and used one-time detection of genital HPV DNA as their outcome of interest (Table 1). Half presented an effect measure adjusted for other covariates, and the length of follow-up was ≤4 years for all but 1 study. The HPV-16 seroprevalence in the studies with female subjects ranged from 6.2% to 45.5%. In random-effect meta-analysis models including female and male subjects, we observed evidence of significant protection against subsequent genital HPV-16 DNA infection comparing HPV-16–seropositive with HPV-16–seronegative individuals ( pooled relative risk [RR], 0.69; 95% confidence interval [CI], .53–.83; Figure 2). Likewise, we observed similar estimates of natural immunity for genital HPV-18 comparing HPV-18– seropositive with HPV-18–seronegative individuals (pooled RR,
Figure 1.
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0.75; 95% CI, .48–1.01; Figure 3) and for non–HPV-16/18 types (6/11/31/33/35/45/52/58) against their respective types (0.75; .57–.92; Figure 4). Combining all measured serotypes, we observed significant natural HPV immunity against their respective type-specific infection (pooled RR, 0.72; 95% CI, .62–.82). We observed differing results by sex. We observed significant HPV-16 and HPV-18 natural immunity in female subjects (HPV-16: pooled RR, 0.65; 95% CI, .50–.80; HPV-18: 0.70; .43–.98) but not in male subjects (HPV-16: 1.22; .67–1.77; HPV-18: 1.50; .46–2.55; Figures 2 and 3). The overall test for heterogeneity comparing female with male subjects approached significance for both HPV-16 (P = .05) and HPV-18 (P = .15). Although there was evidence of potential heterogeneity by sex, there was no evidence for substantial heterogeneity between the 14 individual studies (HPV-16: I 2 = 21.7%; HPV-18: I 2 = 26.8%). There was also no evidence for publication bias for either the HPV-16 analyses (Egger P = .95; Begg P = .79; Supplementary Figure 1) or the HPV-18 analyses (Egger P = .84; Begg P > .99; Supplementary Figure 1). Among studies with female subjects, in the 3 studies using assays that measured only neutralizing antibodies (eg, cLIA), the evidence of HPV-16 and HPV-18 natural immunity was nonsignificantly stronger (HPV-16: RR, 0.46; 95% CI, .24–.68; HPV-18: 0.64; .01–1.27; Figure 5) than in the studies that
Study selection flow diagram for this systematic review and meta-analysis. Abbreviation: HPV, human papillomavirus.
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Table 1.
Description of Studies That Evaluated HPV Natural Immunity in HPV Unvaccinated Individuals
Authors (Year)
Cohort
Age Range at Entry, y
Sex
Location
Sample Size, No. of Subjects
Length of Followup, mo
Serologic Assay
DNA Assay Primers
DNA Outcome Measure
Effect Measure
Variables Adjusted for
HPV Types Tested
HPV-16 Seroprevalence, %
Age at first intercourse, country, marital status, lifetime number of sex partners, smoking, condom usage
HPV-16/18
15.0
Analyzed results by seropositive antibody levels: evidence of stronger protection at higher antibody level
Other Notes
Meta-analysis of HPV Natural Immunity
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Castellsague et al (2014) [6]
Control arm of PATRCIA
15–25
Female Europe, North and South America, Asia, Australia
8193
48
VLP-ELISA
SPF10DEIA/ LIPA
12-mo persistent infection
Adjusted RR
Viscidi et al (2004) [16]
Guanacaste NHS
18–94
Female Costa Rica
6852
84
VLP-ELISA
MY09MY11
1-time detection
Unadjusted RR
. . .
HPV-16/ 18/31
21.8
Initial NHS study —Wentzensen et al (2011) [16] —was a followup
Safaeian et al (2010) [11]
Control arm of CVT
18–25
Female Costa Rica
2813
48
VLP-ELISA
SPF10DEIA/ LIPA
1-time detection
Unadjusted RR
. . .
HPV-16/18
24.8
Analyzed results by seropositive level: evidence of stronger protection at higher antibody level
Velicer et al (2009) [18]
Merck Vaccine Trial
24–45
Female South and North America, Europe, Asia
1858
30
cLIA
multiplex PCR
6-mo persistent infection
Unadjusted RR
. . .
HPV-6/11/ 16/18
18.3
HPV- 16 and HPV18 results were presented combined, suggested potential effect modification by age
Lu et al (2012) [21]
HIM
18–70
Male
Brazil, Mexico, US
1834
18
VLP -ELISA
PGMY09/11
6-mo persistent infection
Adjusted HR
Education, alcohol, smoking, circumcision, lifetime sex partners, partner’s sex
HPV-16
12.9
Mostly heterosexual men, included 211 MSM
Wentzensen et al (2011) [15]
Guanacaste NHS
18–70
Female Costa Rica
912
84
VLP-ELISA and cLIA
MY09MY11
1-time detection
Adjusted OR
Age, sampling adjusted
HPV-6/11/ 16/18
Wilson et al (2014) [14]
ALTS
≥18
Female US
886
24
Luminexbased multiplex
PGMY09/11
6-mo persistent infection
Adjusted OR
New sex partners during course of study
HPV-16/ 18/31/ 33/35/ 45/52/ 58
18.7 (ELISA); 9.7 Suggested cLIA (cLIA) (neutralizing antibody) detects antibodies that are more strongly linked to immunity 23.5
Suggested potential effect modification by recent sexual behavior
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Table 1
continued.
Authors (Year)
Cohort
Age Range at Entry, y
Sex
Location
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Sample Size, No. of Subjects
Length of Followup, mo
719
12
Luminexbased multiplex
SPF10 DEIA/ LIPA 25
1-time detection
Adjusted HR
Serologic Assay
DNA Assay Primers
DNA Outcome Measure
Effect Measure
Variables Adjusted for
HPV Types Tested
HPV-16 Seroprevalence, %
HIV, age, smoking, lifetime sex partner, recent anal sex partner, anal sex position in last 6 mo, circumcision status
HPV-16/18
46.5
HIV-positive and HIV-negative MSM; genital and anal HPV16 outcomes reported
Other Notes
Mooij (2014) [20]
Netherlands MSM
≥18
Male
Malik et al (2009) [19]
Rutgers University
Mean, 20
Female US
508
36
VLP-ELISA
MY09/ MY11
1-time detection
Unadjusted RR
. . .
HPV16/18/ 31/33/ 35/45/ 52/53
15.0
Results for several related alpha groups (not just specific type)
Robbins et al (2014) [23]
CVT
18–25
Female Costa Rica
488
48
GST-L1
LiPA; SPF 10-DEIA
1-time detection
Unadjusted OR
Lifetime number of sex partners at entry
HPV-16/18
NA
CVT follow-up study from Safaeian (2010) [11] with other serologic assay
Viscidi et al (2005) [17]
HERS
26–55
Female US
413
36
VLP-ELISA
MY09MY11 PCR
1-time detection
Unadjusted HR
. . .
HPV16/18/ 31/35/ 45
45.5
Restricted to HIVnegative individuals in this analysis; this study also included HIVpositive results
Lin et al (2013) [24]
CVT
18–25
Female Costa Rica
388
48
ELISA, cLIA, SEAP-NA
SPF 10-HPV 1-time LiPA25 detection
Unadjusted OR
. . .
HPV-16
NA
CVT follow-up study from Safaeian (2010) [11] with other serologic assays
Lu et (2010) [22]
Tucson, AZ, men
18–44
Male
US
285
18
VLP-ELISA
PGMY09/11
1-time detection
Unadjusted IRR
. . .
HPV-16/18
14.4
Men, genital HPV16/18
Ho et al (2002) [25]
Rutgers University
Mean, 20
Female US
242
36
VLP-ELISA
PCR and Southern blot
1-time detection
Adjusted RR
HPV-16
6.2
High levels of IgG for HPV-16 in ≥ 2 previous visits; used HPV-related types (types 16, 31, 33, 35, 52, or 58)
Netherlands
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Age, ethnicity, number of sex partners, duration of sexual relationship, oral contraceptives
Abbreviations: ALTS, ASCUS/LSIL Triage Study; cLIA, competitive Luminex Immunoassay; CVT, Costa Rica Vaccine Trial; ELISA, enzyme-linked immunosorbent assay; HERS, HIV Epidemiology Research Study; HIM, Human Papillomavirus Infection in Men Study; HIV, human immunodeficiency virus; HPV, human papillomavirus; HR, hazard ratio; IgG, immunoglobulin G; IRR, incidence rate ratio; MSM, men who have sex with men; NHS, Natural History Study; OR, odds ratio; PCR, polymerase chain reaction; RR, relative risk; SEAP-NA, secreted alkaline phosphatase neutralization assay; US, United States; VLP, viruslike particle.
Figure 2. Forest plot of the relative risk for human papillomavirus (HPV) type 16 infection comparing HPV-16–seropositive with HPV-16–seronegative individuals. Overall test for heterogeneity comparing studies in male and studies in female subjects: P = .05. Abbreviations: CI, confidence interval; ES, effect size.
measured neutralizing and nonneutralizing antibodies (HPV16: 0.64; .47–.82; HPV-18: 0.71; .39–1.04). In addition, among studies with female subjects, those that tested for HPV DNA using MY09-MY11 consensus primer PCR suggested nonsignificantly stronger natural immunity (HPV-16: RR, 0.51; 95% CI, .21–.82; HPV-18: 0.65; .08–1.22) than those that used the SPF10-DEIA PCR method (HPV-16: 0.74; .58–.89; HPV-18: 0.84; .57–1.11). Likewise, in analyses restricted to female subjects, the point estimates were slightly but nonsignificantly stronger in those using a 6-month persistent HPV DNA end point (HPV-16: RR, 0.59; 95% CI, .41–.77; HPV-18: 0.74; .44–1.03) than in those using a one-time detection end point (HPV-16: 0.69; .59–.78; HPV-18: 0.86; .65–1.07). Finally, results were also nonsignificantly stronger in studies restricted to female subjects that reported adjusted analyses (HPV-16: RR, 0.48; 95% CI, .29–.66; HPV-18: 0.60; .23–.97) than in those that only reported unadjusted analyses (HPV-16: 0.73; .56–.91; HPV-18: 0.77; .36–1.18). DISCUSSION
This systematic review and meta-analysis representing >24 000 individuals finds that HPV antibodies acquired through natural
infection provide protection against subsequent type-specific genital HPV infection. Given that the observed natural immunity is modest and limited to female subjects, coupled with the fact that many HPV-infected individuals do not seroconvert [7, 8, 35], natural immunity is probably inferior to protection obtained from HPV vaccination for formerly infected individuals [36, 37]. There are several reasons why natural HPV immunity may not be as protective as prophylactic HPV vaccination, which has demonstrated high efficacy in formerly HPV-infected individuals [36, 37]. First, the antibody titers/levels in natural immunity are considerably lower than those observed in vaccination [38]. Indeed, a recent analysis of the Costa Rica Vaccine Trial suggested that even women receiving only 1 dose of the HPV-16/18 vaccine had >4 times higher antibody titers than naturally infected women [38]. Although the minimum antibody titer necessary for protection is currently unclear, 2 recent natural immunity studies suggested that protection may be limited to individuals with relatively higher naturally acquired antibody titers [6, 11]. Second, it is possible that misclassification in some of the assays affects the results of these studies. In particular, the VLP-ELISA Meta-analysis of HPV Natural Immunity
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Figure 3. Forest plot of the relative risk for human papillomavirus (HPV) type 18 infection comparing HPV-18–seropositive with HPV-18–seronegative individuals. Overall test for heterogeneity comparing studies in male and studies in female subjects: P = .15. Abbreviations: CI, confidence interval; ES, effect size.
may be prone to misclassification, given that it measures both neutralizing and nonneutralizing antibodies at low levels and has the potential for nonspecific cross-reactivity with other agents. This potential misclassification would attenuate the natural immunity association toward the null. Indeed, in subanalyses restricted to studies using serologic assays that measure only neutralizing antibodies, we observe nonsignificantly stronger protection. However, these serologic assays measuring only neutralizing antibodies are less sensitive measures for cumulative HPV infection [9, 24, 27]. Third, it is possible that the HPV infections observed in these studies could be a mix of newly acquired and reactivated latent infection [39]. Although current PCR-based assay methods cannot distinguish between a potential new acquisition versus a reactivation, a recent study did suggest natural HPV-16 immunity among those with new sex partners (RR, 0.45; 95% CI, .23–.87), but not among those without a new sex partner during followup (1.08; .65–1.79), supporting the possible idea that natural immunity may protect against new acquisition but not reactivation [14]. Protection against new HPV infections is thought to be largely antibody mediated, whereas control of existing infections is probably more cell mediated. Although the strength of 1450
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cell-mediated and humoral immunity against HPV may be correlated, it is possible that antibodies measured in these studies mainly show protection against HPV reacquisition but not reactivation. However, given that the seropositive individuals included in these studies may have already “cleared” an HPV infection before the start of follow-up, their cell-mediated immune responses may also differ from that of seronegative individuals. Therefore, it is conceivable that the protection observed via natural antibodies in serum may only be a surrogate for other local mechanisms that need further elucidation. This systematic review and meta-analysis suggests that HPV natural immunity may be restricted to female subjects. Men are known to have a considerably lower HPV seroprevalence than women [40, 41], and a recent study suggested that HPVseropositive women may have higher antibody levels than HPVseropositive men [26]. This may be because HPV infections in women have more access to the mucosal immune system than HPV infections on the keratinized surface of the male genitals or because HPV detection in men may be more likely to represent deposition instead of infection. However, only 3 relatively modestsized studies in male subjects measured HPV-16 antibody levels (in assays that measured both neutralizing and nonneutralizing
Figure 4. Forest plot of the relative risks for non–human papillomavirus (HPV) type 16 or18 infections comparing those seropositive with those seronegative to the typespecific HPV infection of interest. Abbreviations: CI, confidence interval; ES, effect size.
antibodies), and they were performed separately from the studies in female subjects. Further examination of natural immunity in men is necessary, as well as examination of whether naturally acquired antibodies may protect against extracervical HPV infection, such as oral and anal HPV infection [20, 26], which are known to cause an increasing number of oropharyngeal and anal cancers in higher-income countries [42, 43]. Most of the studies in female subjects that suggested natural immunity were limited to one-time detection of cervical HPV infection, and they followed up the women for ≤4 years. In addition, none of the studies measured the date of the initial
seroconversion, so it is unclear how long antibodies were present before each study’s initiation. Therefore, the duration of natural immunity is still unclear, as well as whether this protection can also be extended against cervical precancer. This meta-analysis suggested nonsignificantly stronger natural immunity when restricted to studies examining HPV persistence as the outcome, and findings of one of the larger studies suggested significant natural immunity against atypical cells of undetermined significance related to HPV-16 and HPV-18 and nonsignificant protection against cervical intraepithelial neoplasia 2+ related to HPV-16 [6]. However, the number of precancers in this study Meta-analysis of HPV Natural Immunity
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Figure 5. Forest plot of the relative risks for human papillomavirus (HPV) type 16 or18 infection comparing HPV-16/18–seropositive with HPV-16/18–seronegative individuals, restricted to studies using assays that measure only neutralizing antibodies. Abbreviations: CI, confidence interval; ES, effect size.
was small, and further examination of the risk of precancer among “HPV-reinfected” individuals is necessary. Understanding the risk of HPV reinfection and subsequent disease is important, given that genital HPV infection is commonly acquired soon after sexual debut [44] and the infection is cleared or controlled in most individuals [2, 3]. Therefore, the number of formerly infected individuals (that may have natural immunity) probably represents a significant proportion of the sexual active population. Indeed, a prevaccine analysis from the US National Health and Nutrition Examination Survey suggested that 20% of women and 9% of men aged ≥20 years were HPV-16 seropositive by VLP-ELISA [41], and subsequent publications suggested that only 5% of women [45] and 6% of men [46] had active HPV-16 infection. Given that this analysis suggested only a modest effect of natural immunity restricted to formerly infected women, it suggests that HPV natural immunity may not have a strong impact on the declining cervical HPV prevalence by age in certain countries [10] or in the reduced cost-effectiveness of HPV vaccination of older individuals [47]. However, the age of participants varied considerably across the different studies included in this meta-analysis, and we were unable to adequately evaluate potential effect modification of natural immunity by age, given the lack of individual person-level data. So, although the lower cervical HPV prevalence at older ages may be more due to a reduced number of new sexual partners with age, we 1452
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cannot exclude a significant impact of natural immunity in certain age ranges [48]. Further study is needed to confirm whether the reduction in sexual partners at older ages has a larger impact on the cost-effectiveness of HPV vaccination in older individuals than the observed natural immunity. Like other systematic reviews and meta-analysis, this study is subject to limitations. Our analysis was unable to examine potential sources of heterogeneity outside of sex, such as age, tobacco use, and HIV status, which could affect the results. We also used studies that had different statistical methods to calculate their effect estimates, including many studies that did not attempt to adjust for any potential confounders. However, results seemed fairly similar when comparing studies that presenting adjusted estimates with those that used unadjusted estimates, although unadjusted estimates may have modestly attenuated to the null. This analysis was also limited in examining natural immunity against types other than HPV-16 and HPV18. Although our natural immunity estimates seemed similar by type, there were few existing studies examining non–HPV-16/ 18 types. Our analyses were restricted to genotype-specific immunity, because further research is necessary to determine whether there may be any natural immunity against phylogenetically related HPV types (ie, “cross-protection”) like what is observed with HPV vaccination [49]. This is the first systematic review and meta-analysis to examine natural HPV immunity in both female and male subjects.
The modest natural immunity observed in this study suggests that many previously exposed unvaccinated individuals are still at risk for future HPV infection and that natural immunity is probably inferior to HPV vaccination in protecting against reinfection. Supplementary Data Supplementary materials are available at http://jid.oxfordjournals.org. Consisting of data provided by the author to benefit the reader, the posted materials are not copyedited and are the sole responsibility of the author, so questions or comments should be addressed to the author. Notes Financial support. This work was supported by the Intramural Research Program of the National Cancer Institute at the National Institutes of Health. Potential conflicts of interest. All authors: No reported conflicts. All authors have submitted the ICMJE Form for Disclosure of Potential Conflicts of Interest. Conflicts that the editors consider relevant to the content of the manuscript have been disclosed. References 1. Baseman JG, Koutsky LA. The epidemiology of human papillomavirus infections. J Clin Virol 2005; 32(suppl 1):S16–24. 2. Schiffman M, Castle PE, Jeronimo J, Rodriguez AC, Wacholder S. Human papillomavirus and cervical cancer. Lancet 2007; 370:890–907. 3. Ho GYF. Natural history of cervicovaginal papillomavirus infection in young women. N Engl J Med 1998; 338:423–8. 4. IARC Working Group on the Evaluation of Carcinogenic Risks to Humans. Human papillomaviruses. IARC Monogr Eval Carcinog Risks Hum 2007; 90:1–636. 5. Rodriguez AC, Schiffman M, Herrero R, et al. Low risk of type-specific carcinogenic HPV re-appearance with subsequent cervical intraepithelial neoplasia grade 2/3. Int J Cancer 2012; 131:1874–81. 6. Castellsague X, Naud P, Chow SN, et al. Risk of newly detected infections and cervical abnormalities in women seropositive for naturally-acquired HPV-16/18 antibodies: analysis of the control arm of PATRICIA. J Infect Dis 2014; 210:517–34. 7. Carter JJ, Koutsky LA, Hughes JP, et al. Comparison of human papillomavirus types 16, 18, and 6 capsid antibody responses following incident infection. J Infect Dis 2000; 181:1911–9. 8. Tong Y, Ermel A, Tu W, Shew M, Brown D. Association of HPV types 6, 11, 16, and 18 DNA detection and serological response in unvaccinated adolescent women. J Med Virol 2013; 85:1786–93. 9. Coseo SE, Porras C, Dodd LE, et al. Evaluation of the polyclonal ELISA HPV serology assay as a biomarker for human papillomavirus exposure. Sex Transm Dis 2011; 38:976–82. 10. Bosch FX, Burchell AN, Schiffman M, et al. Epidemiology and natural history of human papillomavirus infections and type-specific implications in cervical neoplasia. Vaccine 2008; 26(suppl 10):K1–16. 11. Safaeian M, Porras C, Schiffman M, et al. Epidemiological study of anti-HPV16/18 seropositivity and subsequent risk of HPV16 and -18 infections. J Natl Cancer Inst 2010; 102:1653–62. 12. Franceschi S, Baussano I. Naturally-acquired immunity against HPV: why it matters in the HPV vaccine era. J Infect Dis 2014; 210:507–9. 13. Schiller JT, Lowy DR. Understanding and learning from the success of prophylactic human papillomavirus vaccines. Nat Rev Microbiol 2012; 10:681–92. 14. Wilson L, Pawlita M, Castle PE, et al. Seroprevalence of eight oncogenic human papillomaviruses and acquired immunity against re-infection. J Infect Dis 2014; 210:448–55. 15. Wentzensen N, Rodriguez AC, Viscidi R, et al. A competitive serological assay shows naturally acquired immunity to human papillomavirus infections in the Guanacaste Natural History Study. J Infect Dis 2011; 204:94–102. 16. Viscidi RP, Schiffman M, Hildesheim A, et al. Seroreactivity to human papillomavirus (HPV) types 16, 18, or 31 and risk of subsequent HPV infection: results from a population-based study in Costa Rica. Cancer Epidemiol Biomarkers Prev 2004; 13:324–7. 17. Viscidi RP, Snyder B, Cu-Uvin S, et al. Human papillomavirus capsid antibody response to natural infection and risk of subsequent HPV infection in HIV-positive and HIV-negative women. Cancer Epidemiol Biomarkers Prev 2005; 14:283–8.
18. Velicer C, Zhu X, Vuocolo S, Liaw KL, Saah A. Prevalence and incidence of HPV genital infection in women. Sex Transm Dis 2009; 36:696–703. 19. Malik ZA, Hailpern SM, Burk RD. Persistent antibodies to HPV virus-like particles following natural infection are protective against subsequent cervicovaginal infection with related and unrelated HPV. Viral Immunol 2009; 22:445–9. 20. Mooij SH, Landen O, van der Klis FR, et al. No evidence for a protective effect of naturally induced HPV antibodies on subsequent anogenital HPV infection in HIV-negative and HIV-infected MSM. J Infect 2014; 69:375–86. 21. Lu B, Viscidi RP, Wu Y, et al. Prevalent serum antibody is not a marker of immune protection against acquisition of oncogenic HPV16 in men. Cancer Res 2012; 72:676–85. 22. Lu B, Hagensee ME, Lee JH, et al. Epidemiologic factors associated with seropositivity to human papillomavirus type 16 and 18 virus-like particles and risk of subsequent infection in men. Cancer Epidemiol Biomarkers Prev 2010; 19:OF1–6. 23. Robbins HA, Li Y, Porras C, et al. Glutathione S-transferase L1 multiplex serology as a measure of cumulative infection with human papillomavirus. BMC Infect Dis 2014; 14:120. 24. Lin SW, Ghosh A, Porras C, et al. HPV16 seropositivity and subsequent HPV16 infection risk in a naturally infected population: comparison of serological assays. PLoS One 2013; 8:e53067. 25. Ho GY, Studentsov Y, Hall CB, et al. Risk factors for subsequent cervicovaginal human papillomavirus (HPV) infection and the protective role of antibodies to HPV-16 virus-like particles. J Infect Dis 2002; 186:737–42. 26. Beachler DC, Viscidi R, Sugar EA, et al. A longitudinal study of human papillomavirus 16 L1, E6, and E7 seropositivity and oral human papillomavirus 16 infection. Sex Transm Dis 2015; 42:93–7. 27. Dias D, Van Doren J, Schlottmann S, et al. Optimization and validation of a multiplexed Luminex assay to quantify antibodies to neutralizing epitopes on human papillomaviruses 6, 11, 16, and 18. Clin Diagn Lab Immunol 2005; 12:959–69. 28. Harris RJ, Bradburn MJ, Deeks JJ, Harbord DG, Altman DG, Sterne JA. Metan: fixed- and random-effects meta-analysis. Stata J 2008; 8:3–28. 29. Kreimer AR, Clifford GM, Boyle P, Franceschi S. Human papillomavirus types in head and neck squamous cell carcinomas worldwide: a systematic review. Cancer Epidemiol Biomarkers Prev 2005; 14:467–75. 30. Alemany L, Saunier M, Alvarado-Cabrero I, et al. Human papillomavirus DNA prevalence and type distribution in anal carcinomas worldwide. Int J Cancer 2015; 136:98–107. 31. Cochrane handbook for systematic reviews of interventions. Version 5.1.0. 2011. www.cochrane-handbook.org. Accessed 1 September 2015. 32. Egger M, Davey Smith G, Schneider M, Minder C. Bias in meta-analysis detected by a simple, graphical test. BMJ 1997; 315:629–34. 33. Begg CB, Berlin JA. Publication bias: a problem in interpreting medical data. J R Stat Soc Ser A 1988; 151:419–63. 34. Sterne JA. Meta-analysis in Stata: an updated collection from the Stata Journal. College Station, TX: Stata Press, 2009. 35. Giuliano AR, Viscidi RP, Torres BN, et al. Seroconversion following anal and genital HPV infection in men: the HIM study. Papillomavirus Res 2015;1:109–15. 36. Szarewski A, Poppe WA, Skinner SR, et al. Efficacy of the human papillomavirus (HPV)-16/18 AS04-adjuvanted vaccine in women aged 15–25 years with and without serological evidence of previous exposure to HPV-16/18. Int J Cancer 2012; 131:106–16. 37. Beachler DC, Kreimer AR, Schiffman M, et al. Multi-site HPV16/18 vaccine efficacy against cervical, anal, and oral HPV infection. J Natl Cancer Inst 2015; doi:10.1093/ jnci/djv302. 38. Safaeian M, Porras C, Pan Y, et al. Durable antibody responses following one dose of the bivalent human papillomavirus L1 virus-like particle vaccine in the Costa Rica Vaccine Trial. Cancer Prev Res (Phila) 2013; 6:1242–50. 39. Gravitt PE. Evidence and impact of human papillomavirus latency. Open Virol J 2012; 6:198–203. 40. Dunne EF, Nielson CM, Stone KM, Markowitz LE, Giuliano AR. Prevalence of HPV infection among men: a systematic review of the literature. J Infect Dis 2006; 194:1044–57. 41. Stone KM, Karem KL, Sternberg MR, et al. Seroprevalence of human papillomavirus type 16 infection in the United States. J Infect Dis 2002; 186:1396–402. 42. Chaturvedi AK, Engels EA, Pfeiffer RM, et al. Human papillomavirus and rising oropharyngeal cancer incidence in the United States. J Clin Oncol 2011; 29: 4294–301. 43. Shiels MS, Kreimer AR, Coghill AE, Darragh TM, Devesa SS. Anal cancer incidence in the United States, 1977–2011: distinct patterns by histology and behavior. Cancer Epidemiol Biomarkers Prev 2015; 24:1548–56.
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44. Winer RL, Feng Q, Hughes JP, O’Reilly S, Kiviat NB, Koutsky LA. Risk of female human papillomavirus acquisition associated with first male sex partner. J Infect Dis 2008; 197:279–82. 45. Hariri S, Unger ER, Sternberg M, et al. Prevalence of genital human papillomavirus among females in the United States, the National Health And Nutrition Examination Survey, 2003–2006. J Infect Dis 2011; 204:566–73. 46. Giuliano AR, Lee JH, Fulp W, et al. Incidence and clearance of genital human papillomavirus infection in men (HIM): a cohort study. Lancet 2011; 377:932–40.
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47. Kim JJ, Ortendahl J, Goldie SJ. Cost-effectiveness of human papillomavirus vaccination and cervical cancer screening in women older than 30 years in the United States. Ann Intern Med 2009; 151:538–45. 48. Chandra A, Mosher WD, Copen C, Sionean C. Sexual behavior, sexual attraction, and sexual identity in the United States: data from the 2006–2008 National Survey of Family Growth. Natl Health Stat Report 2011:1–36. 49. Herrero R. Human papillomavirus (HPV) vaccines: limited cross-protection against additional HPV types. J Infect Dis 2009; 199:919–22.
Natural Acquired Immunity Against Subsequent Genital Human Papillomavirus Infection: A Systematic Review and Meta-analysis Daniel C. Beachler, Gwendolyne Jenkins, Mahboobeh Safaeian, Aimée R. Kreimer, and Nicolas Wentzensen Division of Cancer Epidemiology, and Genetics, National Cancer Institute, Bethesda, Maryland
Background. Studies have been mixed on whether naturally acquired human papillomavirus (HPV) antibodies may protect against subsequent HPV infection. We performed a systematic review and meta-analysis to assess whether naturally acquired HPV antibodies protect against subsequent genital HPV infection (ie, natural immunity). Methods. We searched the MEDLINE and EMBASE databases for studies examining natural HPV immunity against subsequent genital type-specific HPV infection in female and male subjects. We used random-effects models to derive pooled relative risk (RR) estimates for each HPV type. Results. We identified 14 eligible studies that included >24 000 individuals from 18 countries that examined HPV natural immunity. We observed significant protection against subsequent infection in female subjects with HPV-16 ( pooled RR, 0.65; 95% confidence interval, .50–.80) and HPV-18 (0.70; .43–.98) but not in male subjects (HPV-16: 1.22; .67–1.77 [P = .05 (test for heterogeneity)]; HPV-18: 1.50; .46–2.55; [P = .15]). We also observed type-specific protection against subsequent infection for a combined measure of HPV-6/11/31/33/35/45/52/58 in female subjects ( pooled RR, 0.75; 95% confidence interval, .57–.92). Natural immunity was also evident in female subjects when analyses were restricted to studies that used neutralizing assays, used HPV persistence as an outcome, or reported adjusted analyses (each P < .05). Conclusions. HPV antibodies acquired through natural infection provide modest protection against subsequent cervical HPV infection in female subjects. Keywords. human papillomavirus; antibodies; serology; natural immunity; cervix.
The majority of sexually active individuals acquire ≥1 alphagenus human papillomavirus (HPV) genotype at their genital regions during their lifetime [1]. Although in most individuals the HPV infection can be cleared or controlled within 1 or 2 years [2, 3], HPV persists in the epithelium of a subset of infected individuals and can progress to cancer at several anatomic sites, particularly at the cervix [4]. At least some of the women whose HPV infection is cleared seem to lack lifelong immunity, because type-specific HPV infections can reappear among previously exposed individuals [5]. These HPV reappearances can occasionally progress at least to precancer [5, 6]. In approximately 60%–70% of women who acquire an HPV infection, a measurable type-specific serum antibody response against epitopes develops on the HPV L1 capsid protein [7, 8], representing an insensitive marker of cumulative HPV
Received 27 October 2015; accepted 14 December 2015; published online 21 December 2015. Correspondence: D. C. Beachler, Infections and Immunoepidemiology Branch, Division of Cancer Epidemiology and Genetics, National Cancer Institute, 9609 Medical Center Dr, RM 6-E220, Bethesda, MD 20892 ([email protected]). The Journal of Infectious Diseases® 2016;213:1444–54 Published by Oxford University Press for the Infectious Diseases Society of America 2015. This work is written by (a) US Government employee(s) and is in the public domain in the US. DOI: 10.1093/infdis/jiv753
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exposure [9]. Theoretically, these antibodies could help protect individuals from subsequent infections with that HPV type. Indeed, some have hypothesized that this “natural HPV immunity” may help partially explain the declining cervical HPV prevalence by age seen in some countries [10, 11] and that this immunity could be used as a factor in costeffectiveness models evaluating HPV vaccination of older populations [12]. Protection through naturally acquired polyclonal antibodies is plausible, given that the strong antibodies responses to prophylactic HPV vaccination are believed to be responsible for the protection observed among vaccinated individuals [13]. However, the antibody levels in vaccinated women are orders of magnitude higher than natural antibody levels. Previous study findings seem to be mixed on whether individuals with HPV antibodies acquired from natural HPV infection are protected against subsequent genital HPV infection [6, 11, 14–25]. These studies were often relatively small and used different populations, assays, and analytic techniques that may have affected the discordant results. Therefore we performed a systematic review and meta-analysis of this literature to determine more definitively whether naturally acquired HPV antibodies are protective against subsequent genital HPV infection in unvaccinated individuals.
METHODS Search Strategy and Selection Criteria
We systematically reviewed the biomedical literature for studies conducted between 1 January 1950 and 6 July 2015 using the MEDLINE and EMBASE databases. Key search terms included the following: “human papillomavirus” or “HPV” and “serology” or “viruslike particles” or “seropositivity.” Two of the authors (D. C. B. and G. J.) independently identified eligible publications by reviewing titles and abstracts, and also by searching the reference lists of eligible publications. When an abstract’s content was considered inadequate to determine inclusion, the full text of the article was reviewed. Studies included in the systematic review were required to be longitudinal and needed to evaluate “natural HPV immunity” by testing for HPV L1 serology. Studies must have compared the risk of subsequent genital HPV infection (DNA) among individuals who were HPV seropositive or HPV seronegative at the start of follow-up. We defined HPV natural immunity as HPV antibodies significantly protecting against a subsequent type-specific infection. We did not evaluate whether HPV antibodies protect against subsequent HPV-related types in the same clade (ie, HPV-16 antibodies against HPV-31/33/35/52/ 58 infection). We excluded any studies that did not restrict to individuals who were HPV DNA negative (for the homologous type of interest) at the entry of the analysis. We also restricted analysis to studies that examined genital HPV (DNA) infection as the outcome, because only 2 identifiable studies examined nongenital HPV infection as an outcome [20, 26]. Every other study examining natural immunity against genital HPV infection was included regardless of their study population, including those with human immunodeficiency virus (HIV)–infected individuals. Data Extraction
We extracted data from the included studies using a standardized data-collection form. We included analyses for any alphamucosal HPV genotype. Every included study examined HPV DNA (infection) status measured through polymerase chain reaction (PCR)–based methods with varying primers. Many studies reported multiple outcome results; for this meta-analysis, we used the longest detected infection-level measure (up to 12month persistence) for our main pooled analysis. For example, we used a 6-month persistent HPV infection instead of a onetime detection of HPV for the main pooled analysis when both were presented in an article. However, we also included both results in separate subanalyses specific for 6-month persistent infection and one-time detection. Seven separate publications used the same 3 longitudinal cohort populations. Our main pooled analysis included only 1 publication from each of the 3 populations, selecting the publication using the more sensitive serologic assay (highest percentage of HPV-seropositive individuals) and the largest sample
size, because we were most interested in determining the estimate of protection among all individuals with evidence of previous HPV exposure. Although no current serologic assay seems to be perfectly sensitive for HPV exposure, assays that measure a polyclonal response, such as the viruslike particle enzymelinked immunosorbent assay (VLP-ELISA), seem more sensitive than those that only measure epitope-specific neutralizing antibodies, such as the competitive Luminex Immunoassay (cLIA) [9, 24, 27]. However, in subanalyses examining assayspecific results we included estimates from 2 other publications [15, 24] that compared results using multiple serologic assays. Most studies defined their seropositivity thresholds as 3 or 5 standard deviations above the mean titer/optical density/ intensity level in concurrently tested specimens from virgins, after excluding positive outliers. Some studies presented multiple results using different seropositive cutoff estimates. We used the main cutoff in each article that was presented in the abstract and/or in tables. Data Analysis
Random effect meta-analysis techniques were used to generate pooled summary estimates for HPV-16 and HPV-18 [28]. These 2 HPV types are known to cause approximately 70% of cervical cancer and >80% of HPV-associated noncervical cancers [2, 29, 30]. Natural immunity against 8 alpha HPV types (types 6, 11, 31, 33, 35, 45, 52, and 58) was also each analyzed in a typespecific manner, but these results were then pooled, given that the analyses were restricted to 1–4 publications, depending on the type. A global pooled estimate of natural immunity against all tested HPV types was also calculated. We used adjusted analyses in the meta-analyses when they were available, and we conducted subgroup analysis to examine whether sex may be a source of heterogeneity. We also used the longest detectable HPV infection end point when available (12-month persistent infection in 1 study and 6-month persistent infection in 3). In addition, we performed 4 subgroup analyses, comparing (1) studies that used neutralizing serologic assays (eg, cLIA) with those that used neutralizing and nonneutralizing serologic assay (eg, VLP-ELISA); (2) studies that used MY09-MY11 consensus primer PCR with those that used the SPF10-DEIA PCR method for DNA detection; (3) studies that used a 6-month persistent HPV DNA end point with those that used one-time detection of HPV DNA as an end point; and (4) studies that reported adjusted analyses with those that reported only unadjusted analyses. We examined heterogeneity using the I 2 and χ2 statistics [31], and publication bias using funnel plots and Egger and Begg P values [32, 33], and we performed meta-analyses with Stata SE software (version 13.1; StataCorp) [34]. RESULTS
We systematically searched 1531 articles, and excluded 1490 because the study was not longitudinal, did not test for HPV Meta-analysis of HPV Natural Immunity
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DNA, or did not test for HPV serology. The full texts of each of the remaining 41 studies were reviewed, and 14 articles were identified to meet the inclusion criteria (Figure 1). The included studies spanned 18 countries and included >24 000 HPV unvaccinated individuals (Table 1). Most studies were restricted to female subjects, examining immunity against cervical HPV (11 of 14 publications, approximately 90% of total population) and the majority were conducted in the United States or Costa Rica (10 of 14 publications, approximately 55% of total population). More than half of the studies used the VLP-ELISA as their serologic assay and used one-time detection of genital HPV DNA as their outcome of interest (Table 1). Half presented an effect measure adjusted for other covariates, and the length of follow-up was ≤4 years for all but 1 study. The HPV-16 seroprevalence in the studies with female subjects ranged from 6.2% to 45.5%. In random-effect meta-analysis models including female and male subjects, we observed evidence of significant protection against subsequent genital HPV-16 DNA infection comparing HPV-16–seropositive with HPV-16–seronegative individuals ( pooled relative risk [RR], 0.69; 95% confidence interval [CI], .53–.83; Figure 2). Likewise, we observed similar estimates of natural immunity for genital HPV-18 comparing HPV-18– seropositive with HPV-18–seronegative individuals (pooled RR,
Figure 1.
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0.75; 95% CI, .48–1.01; Figure 3) and for non–HPV-16/18 types (6/11/31/33/35/45/52/58) against their respective types (0.75; .57–.92; Figure 4). Combining all measured serotypes, we observed significant natural HPV immunity against their respective type-specific infection (pooled RR, 0.72; 95% CI, .62–.82). We observed differing results by sex. We observed significant HPV-16 and HPV-18 natural immunity in female subjects (HPV-16: pooled RR, 0.65; 95% CI, .50–.80; HPV-18: 0.70; .43–.98) but not in male subjects (HPV-16: 1.22; .67–1.77; HPV-18: 1.50; .46–2.55; Figures 2 and 3). The overall test for heterogeneity comparing female with male subjects approached significance for both HPV-16 (P = .05) and HPV-18 (P = .15). Although there was evidence of potential heterogeneity by sex, there was no evidence for substantial heterogeneity between the 14 individual studies (HPV-16: I 2 = 21.7%; HPV-18: I 2 = 26.8%). There was also no evidence for publication bias for either the HPV-16 analyses (Egger P = .95; Begg P = .79; Supplementary Figure 1) or the HPV-18 analyses (Egger P = .84; Begg P > .99; Supplementary Figure 1). Among studies with female subjects, in the 3 studies using assays that measured only neutralizing antibodies (eg, cLIA), the evidence of HPV-16 and HPV-18 natural immunity was nonsignificantly stronger (HPV-16: RR, 0.46; 95% CI, .24–.68; HPV-18: 0.64; .01–1.27; Figure 5) than in the studies that
Study selection flow diagram for this systematic review and meta-analysis. Abbreviation: HPV, human papillomavirus.
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Table 1.
Description of Studies That Evaluated HPV Natural Immunity in HPV Unvaccinated Individuals
Authors (Year)
Cohort
Age Range at Entry, y
Sex
Location
Sample Size, No. of Subjects
Length of Followup, mo
Serologic Assay
DNA Assay Primers
DNA Outcome Measure
Effect Measure
Variables Adjusted for
HPV Types Tested
HPV-16 Seroprevalence, %
Age at first intercourse, country, marital status, lifetime number of sex partners, smoking, condom usage
HPV-16/18
15.0
Analyzed results by seropositive antibody levels: evidence of stronger protection at higher antibody level
Other Notes
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Castellsague et al (2014) [6]
Control arm of PATRCIA
15–25
Female Europe, North and South America, Asia, Australia
8193
48
VLP-ELISA
SPF10DEIA/ LIPA
12-mo persistent infection
Adjusted RR
Viscidi et al (2004) [16]
Guanacaste NHS
18–94
Female Costa Rica
6852
84
VLP-ELISA
MY09MY11
1-time detection
Unadjusted RR
. . .
HPV-16/ 18/31
21.8
Initial NHS study —Wentzensen et al (2011) [16] —was a followup
Safaeian et al (2010) [11]
Control arm of CVT
18–25
Female Costa Rica
2813
48
VLP-ELISA
SPF10DEIA/ LIPA
1-time detection
Unadjusted RR
. . .
HPV-16/18
24.8
Analyzed results by seropositive level: evidence of stronger protection at higher antibody level
Velicer et al (2009) [18]
Merck Vaccine Trial
24–45
Female South and North America, Europe, Asia
1858
30
cLIA
multiplex PCR
6-mo persistent infection
Unadjusted RR
. . .
HPV-6/11/ 16/18
18.3
HPV- 16 and HPV18 results were presented combined, suggested potential effect modification by age
Lu et al (2012) [21]
HIM
18–70
Male
Brazil, Mexico, US
1834
18
VLP -ELISA
PGMY09/11
6-mo persistent infection
Adjusted HR
Education, alcohol, smoking, circumcision, lifetime sex partners, partner’s sex
HPV-16
12.9
Mostly heterosexual men, included 211 MSM
Wentzensen et al (2011) [15]
Guanacaste NHS
18–70
Female Costa Rica
912
84
VLP-ELISA and cLIA
MY09MY11
1-time detection
Adjusted OR
Age, sampling adjusted
HPV-6/11/ 16/18
Wilson et al (2014) [14]
ALTS
≥18
Female US
886
24
Luminexbased multiplex
PGMY09/11
6-mo persistent infection
Adjusted OR
New sex partners during course of study
HPV-16/ 18/31/ 33/35/ 45/52/ 58
18.7 (ELISA); 9.7 Suggested cLIA (cLIA) (neutralizing antibody) detects antibodies that are more strongly linked to immunity 23.5
Suggested potential effect modification by recent sexual behavior
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Table 1
continued.
Authors (Year)
Cohort
Age Range at Entry, y
Sex
Location
•
Sample Size, No. of Subjects
Length of Followup, mo
719
12
Luminexbased multiplex
SPF10 DEIA/ LIPA 25
1-time detection
Adjusted HR
Serologic Assay
DNA Assay Primers
DNA Outcome Measure
Effect Measure
Variables Adjusted for
HPV Types Tested
HPV-16 Seroprevalence, %
HIV, age, smoking, lifetime sex partner, recent anal sex partner, anal sex position in last 6 mo, circumcision status
HPV-16/18
46.5
HIV-positive and HIV-negative MSM; genital and anal HPV16 outcomes reported
Other Notes
Mooij (2014) [20]
Netherlands MSM
≥18
Male
Malik et al (2009) [19]
Rutgers University
Mean, 20
Female US
508
36
VLP-ELISA
MY09/ MY11
1-time detection
Unadjusted RR
. . .
HPV16/18/ 31/33/ 35/45/ 52/53
15.0
Results for several related alpha groups (not just specific type)
Robbins et al (2014) [23]
CVT
18–25
Female Costa Rica
488
48
GST-L1
LiPA; SPF 10-DEIA
1-time detection
Unadjusted OR
Lifetime number of sex partners at entry
HPV-16/18
NA
CVT follow-up study from Safaeian (2010) [11] with other serologic assay
Viscidi et al (2005) [17]
HERS
26–55
Female US
413
36
VLP-ELISA
MY09MY11 PCR
1-time detection
Unadjusted HR
. . .
HPV16/18/ 31/35/ 45
45.5
Restricted to HIVnegative individuals in this analysis; this study also included HIVpositive results
Lin et al (2013) [24]
CVT
18–25
Female Costa Rica
388
48
ELISA, cLIA, SEAP-NA
SPF 10-HPV 1-time LiPA25 detection
Unadjusted OR
. . .
HPV-16
NA
CVT follow-up study from Safaeian (2010) [11] with other serologic assays
Lu et (2010) [22]
Tucson, AZ, men
18–44
Male
US
285
18
VLP-ELISA
PGMY09/11
1-time detection
Unadjusted IRR
. . .
HPV-16/18
14.4
Men, genital HPV16/18
Ho et al (2002) [25]
Rutgers University
Mean, 20
Female US
242
36
VLP-ELISA
PCR and Southern blot
1-time detection
Adjusted RR
HPV-16
6.2
High levels of IgG for HPV-16 in ≥ 2 previous visits; used HPV-related types (types 16, 31, 33, 35, 52, or 58)
Netherlands
Beachler et al
Age, ethnicity, number of sex partners, duration of sexual relationship, oral contraceptives
Abbreviations: ALTS, ASCUS/LSIL Triage Study; cLIA, competitive Luminex Immunoassay; CVT, Costa Rica Vaccine Trial; ELISA, enzyme-linked immunosorbent assay; HERS, HIV Epidemiology Research Study; HIM, Human Papillomavirus Infection in Men Study; HIV, human immunodeficiency virus; HPV, human papillomavirus; HR, hazard ratio; IgG, immunoglobulin G; IRR, incidence rate ratio; MSM, men who have sex with men; NHS, Natural History Study; OR, odds ratio; PCR, polymerase chain reaction; RR, relative risk; SEAP-NA, secreted alkaline phosphatase neutralization assay; US, United States; VLP, viruslike particle.
Figure 2. Forest plot of the relative risk for human papillomavirus (HPV) type 16 infection comparing HPV-16–seropositive with HPV-16–seronegative individuals. Overall test for heterogeneity comparing studies in male and studies in female subjects: P = .05. Abbreviations: CI, confidence interval; ES, effect size.
measured neutralizing and nonneutralizing antibodies (HPV16: 0.64; .47–.82; HPV-18: 0.71; .39–1.04). In addition, among studies with female subjects, those that tested for HPV DNA using MY09-MY11 consensus primer PCR suggested nonsignificantly stronger natural immunity (HPV-16: RR, 0.51; 95% CI, .21–.82; HPV-18: 0.65; .08–1.22) than those that used the SPF10-DEIA PCR method (HPV-16: 0.74; .58–.89; HPV-18: 0.84; .57–1.11). Likewise, in analyses restricted to female subjects, the point estimates were slightly but nonsignificantly stronger in those using a 6-month persistent HPV DNA end point (HPV-16: RR, 0.59; 95% CI, .41–.77; HPV-18: 0.74; .44–1.03) than in those using a one-time detection end point (HPV-16: 0.69; .59–.78; HPV-18: 0.86; .65–1.07). Finally, results were also nonsignificantly stronger in studies restricted to female subjects that reported adjusted analyses (HPV-16: RR, 0.48; 95% CI, .29–.66; HPV-18: 0.60; .23–.97) than in those that only reported unadjusted analyses (HPV-16: 0.73; .56–.91; HPV-18: 0.77; .36–1.18). DISCUSSION
This systematic review and meta-analysis representing >24 000 individuals finds that HPV antibodies acquired through natural
infection provide protection against subsequent type-specific genital HPV infection. Given that the observed natural immunity is modest and limited to female subjects, coupled with the fact that many HPV-infected individuals do not seroconvert [7, 8, 35], natural immunity is probably inferior to protection obtained from HPV vaccination for formerly infected individuals [36, 37]. There are several reasons why natural HPV immunity may not be as protective as prophylactic HPV vaccination, which has demonstrated high efficacy in formerly HPV-infected individuals [36, 37]. First, the antibody titers/levels in natural immunity are considerably lower than those observed in vaccination [38]. Indeed, a recent analysis of the Costa Rica Vaccine Trial suggested that even women receiving only 1 dose of the HPV-16/18 vaccine had >4 times higher antibody titers than naturally infected women [38]. Although the minimum antibody titer necessary for protection is currently unclear, 2 recent natural immunity studies suggested that protection may be limited to individuals with relatively higher naturally acquired antibody titers [6, 11]. Second, it is possible that misclassification in some of the assays affects the results of these studies. In particular, the VLP-ELISA Meta-analysis of HPV Natural Immunity
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Figure 3. Forest plot of the relative risk for human papillomavirus (HPV) type 18 infection comparing HPV-18–seropositive with HPV-18–seronegative individuals. Overall test for heterogeneity comparing studies in male and studies in female subjects: P = .15. Abbreviations: CI, confidence interval; ES, effect size.
may be prone to misclassification, given that it measures both neutralizing and nonneutralizing antibodies at low levels and has the potential for nonspecific cross-reactivity with other agents. This potential misclassification would attenuate the natural immunity association toward the null. Indeed, in subanalyses restricted to studies using serologic assays that measure only neutralizing antibodies, we observe nonsignificantly stronger protection. However, these serologic assays measuring only neutralizing antibodies are less sensitive measures for cumulative HPV infection [9, 24, 27]. Third, it is possible that the HPV infections observed in these studies could be a mix of newly acquired and reactivated latent infection [39]. Although current PCR-based assay methods cannot distinguish between a potential new acquisition versus a reactivation, a recent study did suggest natural HPV-16 immunity among those with new sex partners (RR, 0.45; 95% CI, .23–.87), but not among those without a new sex partner during followup (1.08; .65–1.79), supporting the possible idea that natural immunity may protect against new acquisition but not reactivation [14]. Protection against new HPV infections is thought to be largely antibody mediated, whereas control of existing infections is probably more cell mediated. Although the strength of 1450
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cell-mediated and humoral immunity against HPV may be correlated, it is possible that antibodies measured in these studies mainly show protection against HPV reacquisition but not reactivation. However, given that the seropositive individuals included in these studies may have already “cleared” an HPV infection before the start of follow-up, their cell-mediated immune responses may also differ from that of seronegative individuals. Therefore, it is conceivable that the protection observed via natural antibodies in serum may only be a surrogate for other local mechanisms that need further elucidation. This systematic review and meta-analysis suggests that HPV natural immunity may be restricted to female subjects. Men are known to have a considerably lower HPV seroprevalence than women [40, 41], and a recent study suggested that HPVseropositive women may have higher antibody levels than HPVseropositive men [26]. This may be because HPV infections in women have more access to the mucosal immune system than HPV infections on the keratinized surface of the male genitals or because HPV detection in men may be more likely to represent deposition instead of infection. However, only 3 relatively modestsized studies in male subjects measured HPV-16 antibody levels (in assays that measured both neutralizing and nonneutralizing
Figure 4. Forest plot of the relative risks for non–human papillomavirus (HPV) type 16 or18 infections comparing those seropositive with those seronegative to the typespecific HPV infection of interest. Abbreviations: CI, confidence interval; ES, effect size.
antibodies), and they were performed separately from the studies in female subjects. Further examination of natural immunity in men is necessary, as well as examination of whether naturally acquired antibodies may protect against extracervical HPV infection, such as oral and anal HPV infection [20, 26], which are known to cause an increasing number of oropharyngeal and anal cancers in higher-income countries [42, 43]. Most of the studies in female subjects that suggested natural immunity were limited to one-time detection of cervical HPV infection, and they followed up the women for ≤4 years. In addition, none of the studies measured the date of the initial
seroconversion, so it is unclear how long antibodies were present before each study’s initiation. Therefore, the duration of natural immunity is still unclear, as well as whether this protection can also be extended against cervical precancer. This meta-analysis suggested nonsignificantly stronger natural immunity when restricted to studies examining HPV persistence as the outcome, and findings of one of the larger studies suggested significant natural immunity against atypical cells of undetermined significance related to HPV-16 and HPV-18 and nonsignificant protection against cervical intraepithelial neoplasia 2+ related to HPV-16 [6]. However, the number of precancers in this study Meta-analysis of HPV Natural Immunity
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Figure 5. Forest plot of the relative risks for human papillomavirus (HPV) type 16 or18 infection comparing HPV-16/18–seropositive with HPV-16/18–seronegative individuals, restricted to studies using assays that measure only neutralizing antibodies. Abbreviations: CI, confidence interval; ES, effect size.
was small, and further examination of the risk of precancer among “HPV-reinfected” individuals is necessary. Understanding the risk of HPV reinfection and subsequent disease is important, given that genital HPV infection is commonly acquired soon after sexual debut [44] and the infection is cleared or controlled in most individuals [2, 3]. Therefore, the number of formerly infected individuals (that may have natural immunity) probably represents a significant proportion of the sexual active population. Indeed, a prevaccine analysis from the US National Health and Nutrition Examination Survey suggested that 20% of women and 9% of men aged ≥20 years were HPV-16 seropositive by VLP-ELISA [41], and subsequent publications suggested that only 5% of women [45] and 6% of men [46] had active HPV-16 infection. Given that this analysis suggested only a modest effect of natural immunity restricted to formerly infected women, it suggests that HPV natural immunity may not have a strong impact on the declining cervical HPV prevalence by age in certain countries [10] or in the reduced cost-effectiveness of HPV vaccination of older individuals [47]. However, the age of participants varied considerably across the different studies included in this meta-analysis, and we were unable to adequately evaluate potential effect modification of natural immunity by age, given the lack of individual person-level data. So, although the lower cervical HPV prevalence at older ages may be more due to a reduced number of new sexual partners with age, we 1452
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cannot exclude a significant impact of natural immunity in certain age ranges [48]. Further study is needed to confirm whether the reduction in sexual partners at older ages has a larger impact on the cost-effectiveness of HPV vaccination in older individuals than the observed natural immunity. Like other systematic reviews and meta-analysis, this study is subject to limitations. Our analysis was unable to examine potential sources of heterogeneity outside of sex, such as age, tobacco use, and HIV status, which could affect the results. We also used studies that had different statistical methods to calculate their effect estimates, including many studies that did not attempt to adjust for any potential confounders. However, results seemed fairly similar when comparing studies that presenting adjusted estimates with those that used unadjusted estimates, although unadjusted estimates may have modestly attenuated to the null. This analysis was also limited in examining natural immunity against types other than HPV-16 and HPV18. Although our natural immunity estimates seemed similar by type, there were few existing studies examining non–HPV-16/ 18 types. Our analyses were restricted to genotype-specific immunity, because further research is necessary to determine whether there may be any natural immunity against phylogenetically related HPV types (ie, “cross-protection”) like what is observed with HPV vaccination [49]. This is the first systematic review and meta-analysis to examine natural HPV immunity in both female and male subjects.
The modest natural immunity observed in this study suggests that many previously exposed unvaccinated individuals are still at risk for future HPV infection and that natural immunity is probably inferior to HPV vaccination in protecting against reinfection. Supplementary Data Supplementary materials are available at http://jid.oxfordjournals.org. Consisting of data provided by the author to benefit the reader, the posted materials are not copyedited and are the sole responsibility of the author, so questions or comments should be addressed to the author. Notes Financial support. This work was supported by the Intramural Research Program of the National Cancer Institute at the National Institutes of Health. Potential conflicts of interest. All authors: No reported conflicts. All authors have submitted the ICMJE Form for Disclosure of Potential Conflicts of Interest. Conflicts that the editors consider relevant to the content of the manuscript have been disclosed. References 1. Baseman JG, Koutsky LA. The epidemiology of human papillomavirus infections. J Clin Virol 2005; 32(suppl 1):S16–24. 2. Schiffman M, Castle PE, Jeronimo J, Rodriguez AC, Wacholder S. Human papillomavirus and cervical cancer. Lancet 2007; 370:890–907. 3. Ho GYF. Natural history of cervicovaginal papillomavirus infection in young women. N Engl J Med 1998; 338:423–8. 4. IARC Working Group on the Evaluation of Carcinogenic Risks to Humans. Human papillomaviruses. IARC Monogr Eval Carcinog Risks Hum 2007; 90:1–636. 5. Rodriguez AC, Schiffman M, Herrero R, et al. Low risk of type-specific carcinogenic HPV re-appearance with subsequent cervical intraepithelial neoplasia grade 2/3. Int J Cancer 2012; 131:1874–81. 6. Castellsague X, Naud P, Chow SN, et al. Risk of newly detected infections and cervical abnormalities in women seropositive for naturally-acquired HPV-16/18 antibodies: analysis of the control arm of PATRICIA. J Infect Dis 2014; 210:517–34. 7. Carter JJ, Koutsky LA, Hughes JP, et al. Comparison of human papillomavirus types 16, 18, and 6 capsid antibody responses following incident infection. J Infect Dis 2000; 181:1911–9. 8. Tong Y, Ermel A, Tu W, Shew M, Brown D. Association of HPV types 6, 11, 16, and 18 DNA detection and serological response in unvaccinated adolescent women. J Med Virol 2013; 85:1786–93. 9. Coseo SE, Porras C, Dodd LE, et al. Evaluation of the polyclonal ELISA HPV serology assay as a biomarker for human papillomavirus exposure. Sex Transm Dis 2011; 38:976–82. 10. Bosch FX, Burchell AN, Schiffman M, et al. Epidemiology and natural history of human papillomavirus infections and type-specific implications in cervical neoplasia. Vaccine 2008; 26(suppl 10):K1–16. 11. Safaeian M, Porras C, Schiffman M, et al. Epidemiological study of anti-HPV16/18 seropositivity and subsequent risk of HPV16 and -18 infections. J Natl Cancer Inst 2010; 102:1653–62. 12. Franceschi S, Baussano I. Naturally-acquired immunity against HPV: why it matters in the HPV vaccine era. J Infect Dis 2014; 210:507–9. 13. Schiller JT, Lowy DR. Understanding and learning from the success of prophylactic human papillomavirus vaccines. Nat Rev Microbiol 2012; 10:681–92. 14. Wilson L, Pawlita M, Castle PE, et al. Seroprevalence of eight oncogenic human papillomaviruses and acquired immunity against re-infection. J Infect Dis 2014; 210:448–55. 15. Wentzensen N, Rodriguez AC, Viscidi R, et al. A competitive serological assay shows naturally acquired immunity to human papillomavirus infections in the Guanacaste Natural History Study. J Infect Dis 2011; 204:94–102. 16. Viscidi RP, Schiffman M, Hildesheim A, et al. Seroreactivity to human papillomavirus (HPV) types 16, 18, or 31 and risk of subsequent HPV infection: results from a population-based study in Costa Rica. Cancer Epidemiol Biomarkers Prev 2004; 13:324–7. 17. Viscidi RP, Snyder B, Cu-Uvin S, et al. Human papillomavirus capsid antibody response to natural infection and risk of subsequent HPV infection in HIV-positive and HIV-negative women. Cancer Epidemiol Biomarkers Prev 2005; 14:283–8.
18. Velicer C, Zhu X, Vuocolo S, Liaw KL, Saah A. Prevalence and incidence of HPV genital infection in women. Sex Transm Dis 2009; 36:696–703. 19. Malik ZA, Hailpern SM, Burk RD. Persistent antibodies to HPV virus-like particles following natural infection are protective against subsequent cervicovaginal infection with related and unrelated HPV. Viral Immunol 2009; 22:445–9. 20. Mooij SH, Landen O, van der Klis FR, et al. No evidence for a protective effect of naturally induced HPV antibodies on subsequent anogenital HPV infection in HIV-negative and HIV-infected MSM. J Infect 2014; 69:375–86. 21. Lu B, Viscidi RP, Wu Y, et al. Prevalent serum antibody is not a marker of immune protection against acquisition of oncogenic HPV16 in men. Cancer Res 2012; 72:676–85. 22. Lu B, Hagensee ME, Lee JH, et al. Epidemiologic factors associated with seropositivity to human papillomavirus type 16 and 18 virus-like particles and risk of subsequent infection in men. Cancer Epidemiol Biomarkers Prev 2010; 19:OF1–6. 23. Robbins HA, Li Y, Porras C, et al. Glutathione S-transferase L1 multiplex serology as a measure of cumulative infection with human papillomavirus. BMC Infect Dis 2014; 14:120. 24. Lin SW, Ghosh A, Porras C, et al. HPV16 seropositivity and subsequent HPV16 infection risk in a naturally infected population: comparison of serological assays. PLoS One 2013; 8:e53067. 25. Ho GY, Studentsov Y, Hall CB, et al. Risk factors for subsequent cervicovaginal human papillomavirus (HPV) infection and the protective role of antibodies to HPV-16 virus-like particles. J Infect Dis 2002; 186:737–42. 26. Beachler DC, Viscidi R, Sugar EA, et al. A longitudinal study of human papillomavirus 16 L1, E6, and E7 seropositivity and oral human papillomavirus 16 infection. Sex Transm Dis 2015; 42:93–7. 27. Dias D, Van Doren J, Schlottmann S, et al. Optimization and validation of a multiplexed Luminex assay to quantify antibodies to neutralizing epitopes on human papillomaviruses 6, 11, 16, and 18. Clin Diagn Lab Immunol 2005; 12:959–69. 28. Harris RJ, Bradburn MJ, Deeks JJ, Harbord DG, Altman DG, Sterne JA. Metan: fixed- and random-effects meta-analysis. Stata J 2008; 8:3–28. 29. Kreimer AR, Clifford GM, Boyle P, Franceschi S. Human papillomavirus types in head and neck squamous cell carcinomas worldwide: a systematic review. Cancer Epidemiol Biomarkers Prev 2005; 14:467–75. 30. Alemany L, Saunier M, Alvarado-Cabrero I, et al. Human papillomavirus DNA prevalence and type distribution in anal carcinomas worldwide. Int J Cancer 2015; 136:98–107. 31. Cochrane handbook for systematic reviews of interventions. Version 5.1.0. 2011. www.cochrane-handbook.org. Accessed 1 September 2015. 32. Egger M, Davey Smith G, Schneider M, Minder C. Bias in meta-analysis detected by a simple, graphical test. BMJ 1997; 315:629–34. 33. Begg CB, Berlin JA. Publication bias: a problem in interpreting medical data. J R Stat Soc Ser A 1988; 151:419–63. 34. Sterne JA. Meta-analysis in Stata: an updated collection from the Stata Journal. College Station, TX: Stata Press, 2009. 35. Giuliano AR, Viscidi RP, Torres BN, et al. Seroconversion following anal and genital HPV infection in men: the HIM study. Papillomavirus Res 2015;1:109–15. 36. Szarewski A, Poppe WA, Skinner SR, et al. Efficacy of the human papillomavirus (HPV)-16/18 AS04-adjuvanted vaccine in women aged 15–25 years with and without serological evidence of previous exposure to HPV-16/18. Int J Cancer 2012; 131:106–16. 37. Beachler DC, Kreimer AR, Schiffman M, et al. Multi-site HPV16/18 vaccine efficacy against cervical, anal, and oral HPV infection. J Natl Cancer Inst 2015; doi:10.1093/ jnci/djv302. 38. Safaeian M, Porras C, Pan Y, et al. Durable antibody responses following one dose of the bivalent human papillomavirus L1 virus-like particle vaccine in the Costa Rica Vaccine Trial. Cancer Prev Res (Phila) 2013; 6:1242–50. 39. Gravitt PE. Evidence and impact of human papillomavirus latency. Open Virol J 2012; 6:198–203. 40. Dunne EF, Nielson CM, Stone KM, Markowitz LE, Giuliano AR. Prevalence of HPV infection among men: a systematic review of the literature. J Infect Dis 2006; 194:1044–57. 41. Stone KM, Karem KL, Sternberg MR, et al. Seroprevalence of human papillomavirus type 16 infection in the United States. J Infect Dis 2002; 186:1396–402. 42. Chaturvedi AK, Engels EA, Pfeiffer RM, et al. Human papillomavirus and rising oropharyngeal cancer incidence in the United States. J Clin Oncol 2011; 29: 4294–301. 43. Shiels MS, Kreimer AR, Coghill AE, Darragh TM, Devesa SS. Anal cancer incidence in the United States, 1977–2011: distinct patterns by histology and behavior. Cancer Epidemiol Biomarkers Prev 2015; 24:1548–56.
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•
JID 2016:213 (1 May)
•
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44. Winer RL, Feng Q, Hughes JP, O’Reilly S, Kiviat NB, Koutsky LA. Risk of female human papillomavirus acquisition associated with first male sex partner. J Infect Dis 2008; 197:279–82. 45. Hariri S, Unger ER, Sternberg M, et al. Prevalence of genital human papillomavirus among females in the United States, the National Health And Nutrition Examination Survey, 2003–2006. J Infect Dis 2011; 204:566–73. 46. Giuliano AR, Lee JH, Fulp W, et al. Incidence and clearance of genital human papillomavirus infection in men (HIM): a cohort study. Lancet 2011; 377:932–40.
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•
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47. Kim JJ, Ortendahl J, Goldie SJ. Cost-effectiveness of human papillomavirus vaccination and cervical cancer screening in women older than 30 years in the United States. Ann Intern Med 2009; 151:538–45. 48. Chandra A, Mosher WD, Copen C, Sionean C. Sexual behavior, sexual attraction, and sexual identity in the United States: data from the 2006–2008 National Survey of Family Growth. Natl Health Stat Report 2011:1–36. 49. Herrero R. Human papillomavirus (HPV) vaccines: limited cross-protection against additional HPV types. J Infect Dis 2009; 199:919–22.
