J Infect Chemother 20 (2014) 238e242
Contents lists available at ScienceDirect
Journal of Infection and Chemotherapy journal homepage: http://www.elsevier.com/locate/jic
Original article
Immunogenicity of single-dose Vero cell-derived Japanese encephalitis vaccine in Japanese adults Nozomi Takeshita, MD a, *, Chang-Kweng Lim b, Yasutaka Mizuno c, Takuro Shimbo d, Akira Kotaki b, Mugen Ujiie a, Kayoko Hayakawa a, Yasuyuki Kato a, Shuzo Kanagawa a, Mitsuo Kaku e, Tomohiko Takasaki b a
Disease Control and Prevention Center, National Center for Global Health and Medicine, 1-21-1 Toyama, Shinjuku-ku, Tokyo 162-8655, Japan Department of Virology 1, National Institute of Infectious Diseases, Tokyo, Japan Department of Infection Control and Prevention, Tokyo Medical University, Japan d Department of Clinical Research and Informatics, International Clinical Research Center, National Center for Global Health and Medicine, 1-21-1 Toyama, Shinjuku-ku, Tokyo 162-8655, Japan e Department of Infection Control and Laboratory Diagnostics, Internal Medicine, Tohoku University Graduate School of Medicine, Sendai, Japan b c
a r t i c l e i n f o
a b s t r a c t
Article history: Received 22 August 2013 Received in revised form 25 November 2013 Accepted 28 November 2013
In Japan, intensive immunization against Japanese encephalitis (JE) was performed from 1967 to 1976, and regular JE immunization was performed thereafter. However, for Japanese adults facing JE risk, dates of vaccination with new inactivated Vero cell-derived JE vaccine are unavailable. This study investigated how a single dose of Vero cell-derived JE vaccine affects Japanese adults. Neutralizing antibodies were measured pre- and post-JE vaccination in 79 participants (age 40.7 9.4 years), enrolled between October 2009 and March 2011, whose JE-vaccination data were gathered from vaccination records and history taking. Before vaccination, the participants’ seroprotection rate (SPR) was 51.9%, whereas SPR after vaccination was 93.7%. The seroconversion rate (SCR), which measures seronegative cases that turn seropositive after vaccination, was 86.8%. The geometric mean titer (GMT) was 14.7 before vaccination and 70.1 after vaccination. Age was a significant difference between seroprotected (42.8 years) and nonseroprotected (38.7 years) groups before vaccination. Then the difference of age, SCR, pre-vaccination GMT, post-vaccination GMT and sex ratio were also significant in participants aged 25e39 years and 40 years, who represent generations born when Japan’s JE-vaccination policy changed. SCR was 100% in participants aged 25e39 years with a vaccination recorded 55.6% in participants aged 25e39 without a vaccination record, and 96.0% in participants aged 40 years. Thus, more participants aged 25e39 years were seroprotected before vaccination, but SCR was higher in those aged 40 years. Most Japanese adults can be protected after one-dose vaccination, but this may be insufficient for people aged 25e39 years without recorded JE vaccination. Ó 2014, Japanese Society of Chemotherapy and The Japanese Association for Infectious Diseases. Published by Elsevier Ltd. All rights reserved.
Keywords: Japanese encephalitis Vero cells Japanese Travel vaccine
1. Introduction Japanese encephalitis (JE) is endemic in Asian countries. Over 20,000 JE cases have been reported in Asia, but this may underestimate the real number of people with JE [1]. There is no specific * Corresponding author. Tel.: þ81 3 3202 7181; fax: þ81 3 3207 1038. E-mail addresses: [email protected] (N. Takeshita), [email protected] (C.-K. Lim), [email protected] (Y. Mizuno), [email protected] (T. Shimbo), [email protected] (A. Kotaki), infi[email protected] (M. Ujiie), [email protected] (K. Hayakawa), [email protected] (Y. Kato), [email protected] (S. Kanagawa), [email protected] (M. Kaku), [email protected] (T. Takasaki).
treatment for JE, but vaccination is effective in preventing JE. The World Health Organization (WHO) and the U.S. Advisory Committee on Immunization Practice (ACIP) recommends JE vaccines for travelers who visit areas where JE is endemic [2,3]. There were 55 cases of JE in people who traveled from non-endemic areas to endemic areas between 1973 and 2008 and 2 cases in 2010 [4e6]; although these numbers are small, 11 of the patients (19.2%) died. ACIP recommends a primary vaccination series for JE of 3 doses administered on days 0, 7, and 30 [3]. While the WHO recommends the 3-primary series or, alternatively, 2 primary doses preferably 4 weeks apart [2]. The 2-primary-dose schedule followed by a booster after 1 year is used in many Asian countries including
1341-321X/$ e see front matter Ó 2014, Japanese Society of Chemotherapy and The Japanese Association for Infectious Diseases. Published by Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.jiac.2013.11.010
N. Takeshita et al. / J Infect Chemother 20 (2014) 238e242
Japan. However, the effect of the booster vaccine on people vaccinated previously for JE and on those who live in areas where JE is endemic areas is not clear, especially in relation to the use of the newly approved, inactivated Vero cell-derived JE vaccine for adults. The number of JE cases in Japan has decreased from over 1000 in the late 1960s to less than 10 cases after 1992 [7]. This fall in the number of JE cases in Japan may be because of these reasons: One, the mouse brain-derived, inactivated JE vaccine, which was approved in 1954 and has been used in the recommended 3-shot vaccination series 1976, is considered effective in reducing JE infection. Two, the population of the vector mosquito has decreased because their larvae do not survive in the paddy fields used for cultivating rice [8]. Lastly, pig farms have been moved away from residential areas [9]. In the JE-vaccination program of Japan since 1976, this program had three step components (Fig. 1). The recommendation to administer the 3rd booster was terminated on July 29, 2005. The rate of JE vaccination between 1977 and 1995 ranged from 42% to 66%, with approximately 80% vaccination in high-risk areas [1]. In May 2005, the Ministry of Health, Labour and Welfare (MHLW) of Japan suspended the strong recommendation for JE vaccination, because the JE vaccine was suspected to be associated with the adverse effects of acute disseminated encephalomyelitis [10]. After evaluating the safety and effectiveness of Vero cell-derived JE vaccine in clinical studies, the Vero cell-derived JE vaccine was approved, and routine vaccination was resumed in 2009 [11,12]. MHLW reports that the JE vaccination rate was approximately 80% between 1995 and 2004 [13]. More specifically, a report in 2008 showed that the percentage of Japanese who had a neutralizing antibody titer of 10 in JE [2]. 2.3. Vaccination and examination
2. Participants and methods
For measuring antibodies, serum was obtained from each subject before vaccination and 3e5 weeks after vaccination. Immunization history was determined by interviewing the subject or from the subject’s immunization record.
2.1. Participants
2.4. Statistical analysis
From October 2009 to March 2011, we recruited 113 Japanese who received JE vaccination at the National Center for Global Health and Medicine (NCGM), Tokyo, Japan. Neutralization
For differences in seroconversion rate (SCR) and geometric mean titer (GMT) of the neutralizing antibody, 95%-confidence intervals expressed as a 2-sided range were calculated for pre- and
Fig. 1. The JE-vaccination program of Japan. The primary vaccination is administrated twice at 1e4-week intervals between the ages of 6 and 90 months. The first booster vaccination is administered 1 year after the primary vaccination (1st step). The 2nd booster is administered between the ages of 9 and 13 years (2nd step), and the 3rd booster was administered during the ages of 14e15 years (3rd step).
240
N. Takeshita et al. / J Infect Chemother 20 (2014) 238e242
post-vaccination periods, and the 2 factors related this study, age and immunization history, were analyzed. For immunization history, we compared 3 groups: (1) persons with a history of JE vaccination and an immunization record (record group); (2) persons with a history of JE vaccination only (history group); and (3) persons who were not vaccinated with JE vaccine or could not confirm their vaccination history (unknown group). For age, we compared 25e39-years group and 40-years groups. Significance of differences in SCR was assessed using the Chi-square test, and significance of differences in GMT was assessed using the t test. A value of p < 0.05 was considered statistically significant. STATA Version 11 (Stata Corp LP, College Station, TX, USA) was used for all statistical analyses. This study was approved by the Institutional Review Board of the NCGM. (the Institutional Review Board of the NCGM number 689). 3. Results 3.1. Study participants’ dispositions and demographics The 79 study participants as a group were aged 40.7 9.4 years and included 54 males (68.4%); 13 (16.5%) participants were in the record group, 37 (46.8%) participants in the history group, and 29 (36.7%) in the unknown group (Table 1). In the record group, 8 participants had vaccinations 3 times, and the rest 2 times. Before vaccination, 38 (48.1%) participants were negative for the JE NT-Ab and 41 (51.9%) were positive for JE NT-Ab. Age was significantly different (p ¼ 0.02) between these groups: 42.8 8.5 years for the JE NT-Ab-negative group and 38.7 10.0 years for the JE NT-Ab-positive group. However, immunization history and frequency were not significantly different (Table 1). 3.2. Change in seroprotection rate (SPR) before and after vaccination The SPR was increased significantly by vaccination, going from 51.8% (n ¼ 41) before vaccination to 83.7% (n ¼ 74) after vaccination (Table 2). In the JE NT-Ab-negative group, 33 out of the 38 participants changed from negative to positive, an SCR of 86.8%. In the JE NT-Ab-positive group, antibody titers of 26 out of the 41 participants (63.4%) increased more than 4 fold after vaccination. For all participants, GMT increased from 14.7 to 70.1 after vaccination, and the geometric mean fold rise (GMFR) was 4.76 (Table 2). In the JE NT-Ab-negative group, 33 participants underwent seroconversion and 5 participants did not, but their ages, sex, immunization history, and frequency of past vaccination were not significantly different. Table 1 Characteristics of participants and JE immunization history. Characteristic
Age (mean SD) Male/Female Previous immunization recorda Previous immunization historyb (no record) Unknown record/history Previous JE-MB vaccine 3 doses 2 doses
Table 2 Effects of receiving inactivated Vero cell culture-derived Japanese encephalitis vaccine. Total (n ¼ 79) Pre-seroprotection rate (n) Post-seroprotection rate (n) Seroconversion rate (n) Pre-GMT (CI) Post-GMT (CI) GMFR (CI) Geometric titer 4-fold (%)
51.9% (41/79) 93.7% (74/79) 86.8% (33/38) 14.7 (10.9e19.9) 70.1 (47.6e103) 4.76 (3.76e6.06) 26/41 (63.4%)
3.3. Comparison of immunization history The record, history, and unknown groups had 13 (16.5%), 37 (46.8%), and 29 (36.7%) participants, respectively, and average ages for these groups were significantly different (p ¼ 0.00): 34.6 2.87 years for the record group, 39 1.19 years for the history group, 45.6 1.76 years for the unknown group. However, significant differences were not found in SPR before and after vaccination, SCR, GMT before and after vaccination, and GMFR (Table 3). 3.4. Comparison of age groups The GMT before vaccination was 14.7 (25e39 years, 22.0; 40 years, 10.5; p ¼ 0.02) and after vaccination was 70.1 (25e39 years, 129; 40 years, 42; p ¼ 0.01), being significantly higher in the 25e 39-years group than in the 40-years group. GMFR was 4.76 and again higher in the 25e39 years group, but the difference between groups was not statistically significant (25e39 years, 5.90; 40 years, 4.00; p ¼ 0.13). Moreover, 63.4% of the participants showed a 4-fold or greater increase in GMT from before to after vaccination, and although the rate was higher in the 25e39-years group, the difference between groups was not statistically significant (25e39 years, 73.9%; 40 years, 50.0%; p ¼ 0.12). The SCR was significantly different for the two groups (25e39 years, 69.2%; 40 years, 96.0%; p ¼ 0.04) (Table 4). 3.5. Participants with reliable immunization records For the 13 participants with confirmed vaccination records, the SPR was 53.8% before vaccination and 100% after vaccination, and the SCR was 100% (Table 3). For the 25e39-years group, the SPR was 63.9% before vaccination (history and unknown groups, 65.4%; record groups, 60.0%) and 88.9% after vaccination (history and unknown groups, 84.6%; record groups, 100%), and the SCR was 69.2% (history and unknown groups, 9 participants, 55.6%; record groups, 4 participants, 100%). 4. Discussion
Total (n ¼ 79)
JE NT-Abc negative (n ¼ 38)
JE NT-Ab positive (n ¼ 41)
p
40.7 9.4 54/25 13 37
42.8 8.5 27/11 6 19
38.7 10.0 27/14 7 18
0.02** 0.64* 1.00* 0.66*
29
13
16
0.82*
8 5
4 2
4 3
1.00* 1.00*
*The p-value was calculated using Fisher test. **The p-value was calculated using Manh-Whitney analysis. a Confirmed with documents. b Confirmed by history taking only. c JE NT-Ab ¼ Japanese encephalitis Neutralizing antibodies.
This study found that the mean age of the JE NT-Ab-negative group was 42.8 years, and SPR of the JE NT-Ab-positive group before vaccination was 63.9% for 25e39-years group and 41.9% for the 40-years group. These results are almost identical to those of JE surveillance in 2011 [17]. The immunity provided by vaccination can decrease with time. The random coefficient model suggests that the JE NT-Ab decreases by approximately 80%, changing to negative over 15 years [18], which means that other factors may be responsible for the higher SPR in the of elderly population than in the 40-years group; these factors may include differences in JEvaccination programs and the probability of natural infection in older people. Specifically, before 1966, more than 1000 cases of JE were reported in Japan [7,9], and from 1967 to 1974, a special JEvaccination program was conducted for children. During that time,
N. Takeshita et al. / J Infect Chemother 20 (2014) 238e242
241
Table 3 Seroprotection rates and geometric mean titers (GMT) in participants receiving inactivated Vero cell culture-derived Japanese encephalitis vaccine. Characteristic
Previous immunization record (n ¼ 13)
Previous immunization history only (n ¼ 37)
Unknown record/ history (n ¼ 29)
p
Age (mean, in years) Male/female Pre-seroprotection rate (n) Post-seroprotection rate (n) Seroconversion rate (n) Pre-GMT (CI) Post-GMT (CI) GMFR (CI) Geometric titer 4-fold % (CI)
34.6 2.87 8/5 53.8% (7/13) 100% (13/13) 100% (6/6) 19.0 (7.26e49.6) 151.4 (46.6e492) 8 (4.23e15.1) 71.4% (5/7)
39 1.19 23/14 48.6% (18/37) 83.8% (31/37) 78.9% (15/19) 14.8 (9.14e23.9) 60.2 (32.7e111) 4.08 (2.89e5.78) 66.7% (12/18)
45.6 1.76 23/6 55.2% (16/29) 96.6% (28/29) 92.3% (12/13) 13.0 (8.45e20.0) 60.0 (34.8e103) 4.63 (3.07e6.92) 56.3% (9/16)
0.00** 0.28* 0.86* 0.28* 0.32* 0.85** 0.31** 0.14** 0.73*
*The p-value was calculated using Chi-square test. **The p-value was calculated using KruskaleWallis analysis.
the recommended vaccination schedule was 2 doses with an interval of 7e10 days and a single booster dose just before the peak season; however, the booster varied regionally, every year in some areas, every 3e4 years in other areas [19,20]. This booster timing was one of the different points from regular vaccination program. After that vaccination program ended, a regular vaccination program was started. These reasons may account for the differences between the 25e39-years group and the 40-years group. The results of this study showed that most Japanese adults are protected effectively after one dose of Vero cell-derived JE vaccination. The efficacies of mouse brain-derived and Vero cell-derived JE vaccine were found to be similar for JE NT-Ab-negative adults [11]. Moreover, a single dose of Vero cell-derived JE vaccine (IxaaroÒ), which used aluminum hydroxide as the adjuvant, was effective in people who were previously vaccinated with inactivated mouse brain-derived JE vaccine [21,22]. Although immunization histories should be confirmed by documents, such confirmation was not possible in the case of many participants in this study, with records being available for only 16.5% of the participants. Because most people find it difficult to remember their immunization history from childhood, a public records system should be devised for maintaining JE immunization history accurately, as with other vaccinations. For the 13 participants with a definitive immunization history, SPR before vaccination was 53.8% and after vaccination was 100%, and the SCR was 100%. In this group, 10 participants were aged 20e39 years and 3 were aged 40 years. Although the number of participants with a definitive immunization history in this study was low, our findings suggest that one vaccination with the JE vaccine is adequately effective in this particular group. When comparing the two age groups, SPR before vaccination was significantly higher in the 25e 39-years group, whereas SPRs after vaccination with Vero cellderived vaccine were similar for the two groups. Accordingly, Table 4 Seroprotection rate and geometric mean titer of participants receiving JE vaccination. Variable
25e39 years old n ¼ 36)
40 years old (n ¼ 43)
p
Age (mean value in years) Male/female Pre-seroprotection rate Post-seroprotection rate Seroconversion rate Pre-GMT (CI) Post-GMT (CI) GMFR (CI) Geometric titer 4-fold
32.6 4.4 20/16 63.9% (23/36) 88.9% (32/36) 69.2% (9/13) 22.0 (13.1e37.1) 129 (67.3e249) 5.90 (3.97e8.69) 73.9% (17/23)
47.5 6.8 34/9 41.9% (18/43) 97.7% (42/43) 96.0% (24/25) 10.5 (7.52e14.7) 42.0 (27.7e63.6) 4.00 (2.99e5.35) 50.0% (9/18)
0.00** 0.02* 0.07* 0.17* 0.04* 0.02** 0.01** 0.13** 0.19*
*The p-value was calculated using Fisher test. **The p-value was calculated using Manh-Whitney analysis.
SCRs for the 25e39-years and 40-years groups were 69.2% and 96.0%, respectively, and the difference was statistically significant. The above results indicate that vaccination rates in people aged 25e39 years and the current prevalence of subclinical JE infection must be investigated. The 1st-step vaccination rate for JE virus reached approximately 80% by 2004 [13]. However, during 2005 and 2006, when JE vaccination was not recommended strongly, vaccination rates dropped to 22.1% and 4.0%, respectively, even for the 1st step [13]. Regular vaccination with Vero cell-derived JE vaccine has been recommended strongly since April 2010, but the additional vaccination rates for children aged 76 months (at the 1st step of 2primary vaccinations) were as low as 15.5% in 2009 and 30.6% in 2010, and the SPRs in these children in the future is anticipated to be lower than those recorded in previous surveys [23]. Currently, subclinical JE infection is considered to be widespread in Western Japan, where more cases of JE were reported previously, than in the eastern part of Japan, including Tokyo. However, surveys on JE antibodies conducted on children without vaccination history in West and East Japan found the same, approximately 10%, JE NTAb-positive rates in both areas [24]. In a 2008 survey of 3200 participants conducted in 11 prefectures of Japan, evaluation of unvaccinated participants showed that SPR was
Contents lists available at ScienceDirect
Journal of Infection and Chemotherapy journal homepage: http://www.elsevier.com/locate/jic
Original article
Immunogenicity of single-dose Vero cell-derived Japanese encephalitis vaccine in Japanese adults Nozomi Takeshita, MD a, *, Chang-Kweng Lim b, Yasutaka Mizuno c, Takuro Shimbo d, Akira Kotaki b, Mugen Ujiie a, Kayoko Hayakawa a, Yasuyuki Kato a, Shuzo Kanagawa a, Mitsuo Kaku e, Tomohiko Takasaki b a
Disease Control and Prevention Center, National Center for Global Health and Medicine, 1-21-1 Toyama, Shinjuku-ku, Tokyo 162-8655, Japan Department of Virology 1, National Institute of Infectious Diseases, Tokyo, Japan Department of Infection Control and Prevention, Tokyo Medical University, Japan d Department of Clinical Research and Informatics, International Clinical Research Center, National Center for Global Health and Medicine, 1-21-1 Toyama, Shinjuku-ku, Tokyo 162-8655, Japan e Department of Infection Control and Laboratory Diagnostics, Internal Medicine, Tohoku University Graduate School of Medicine, Sendai, Japan b c
a r t i c l e i n f o
a b s t r a c t
Article history: Received 22 August 2013 Received in revised form 25 November 2013 Accepted 28 November 2013
In Japan, intensive immunization against Japanese encephalitis (JE) was performed from 1967 to 1976, and regular JE immunization was performed thereafter. However, for Japanese adults facing JE risk, dates of vaccination with new inactivated Vero cell-derived JE vaccine are unavailable. This study investigated how a single dose of Vero cell-derived JE vaccine affects Japanese adults. Neutralizing antibodies were measured pre- and post-JE vaccination in 79 participants (age 40.7 9.4 years), enrolled between October 2009 and March 2011, whose JE-vaccination data were gathered from vaccination records and history taking. Before vaccination, the participants’ seroprotection rate (SPR) was 51.9%, whereas SPR after vaccination was 93.7%. The seroconversion rate (SCR), which measures seronegative cases that turn seropositive after vaccination, was 86.8%. The geometric mean titer (GMT) was 14.7 before vaccination and 70.1 after vaccination. Age was a significant difference between seroprotected (42.8 years) and nonseroprotected (38.7 years) groups before vaccination. Then the difference of age, SCR, pre-vaccination GMT, post-vaccination GMT and sex ratio were also significant in participants aged 25e39 years and 40 years, who represent generations born when Japan’s JE-vaccination policy changed. SCR was 100% in participants aged 25e39 years with a vaccination recorded 55.6% in participants aged 25e39 without a vaccination record, and 96.0% in participants aged 40 years. Thus, more participants aged 25e39 years were seroprotected before vaccination, but SCR was higher in those aged 40 years. Most Japanese adults can be protected after one-dose vaccination, but this may be insufficient for people aged 25e39 years without recorded JE vaccination. Ó 2014, Japanese Society of Chemotherapy and The Japanese Association for Infectious Diseases. Published by Elsevier Ltd. All rights reserved.
Keywords: Japanese encephalitis Vero cells Japanese Travel vaccine
1. Introduction Japanese encephalitis (JE) is endemic in Asian countries. Over 20,000 JE cases have been reported in Asia, but this may underestimate the real number of people with JE [1]. There is no specific * Corresponding author. Tel.: þ81 3 3202 7181; fax: þ81 3 3207 1038. E-mail addresses: [email protected] (N. Takeshita), [email protected] (C.-K. Lim), [email protected] (Y. Mizuno), [email protected] (T. Shimbo), [email protected] (A. Kotaki), infi[email protected] (M. Ujiie), [email protected] (K. Hayakawa), [email protected] (Y. Kato), [email protected] (S. Kanagawa), [email protected] (M. Kaku), [email protected] (T. Takasaki).
treatment for JE, but vaccination is effective in preventing JE. The World Health Organization (WHO) and the U.S. Advisory Committee on Immunization Practice (ACIP) recommends JE vaccines for travelers who visit areas where JE is endemic [2,3]. There were 55 cases of JE in people who traveled from non-endemic areas to endemic areas between 1973 and 2008 and 2 cases in 2010 [4e6]; although these numbers are small, 11 of the patients (19.2%) died. ACIP recommends a primary vaccination series for JE of 3 doses administered on days 0, 7, and 30 [3]. While the WHO recommends the 3-primary series or, alternatively, 2 primary doses preferably 4 weeks apart [2]. The 2-primary-dose schedule followed by a booster after 1 year is used in many Asian countries including
1341-321X/$ e see front matter Ó 2014, Japanese Society of Chemotherapy and The Japanese Association for Infectious Diseases. Published by Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.jiac.2013.11.010
N. Takeshita et al. / J Infect Chemother 20 (2014) 238e242
Japan. However, the effect of the booster vaccine on people vaccinated previously for JE and on those who live in areas where JE is endemic areas is not clear, especially in relation to the use of the newly approved, inactivated Vero cell-derived JE vaccine for adults. The number of JE cases in Japan has decreased from over 1000 in the late 1960s to less than 10 cases after 1992 [7]. This fall in the number of JE cases in Japan may be because of these reasons: One, the mouse brain-derived, inactivated JE vaccine, which was approved in 1954 and has been used in the recommended 3-shot vaccination series 1976, is considered effective in reducing JE infection. Two, the population of the vector mosquito has decreased because their larvae do not survive in the paddy fields used for cultivating rice [8]. Lastly, pig farms have been moved away from residential areas [9]. In the JE-vaccination program of Japan since 1976, this program had three step components (Fig. 1). The recommendation to administer the 3rd booster was terminated on July 29, 2005. The rate of JE vaccination between 1977 and 1995 ranged from 42% to 66%, with approximately 80% vaccination in high-risk areas [1]. In May 2005, the Ministry of Health, Labour and Welfare (MHLW) of Japan suspended the strong recommendation for JE vaccination, because the JE vaccine was suspected to be associated with the adverse effects of acute disseminated encephalomyelitis [10]. After evaluating the safety and effectiveness of Vero cell-derived JE vaccine in clinical studies, the Vero cell-derived JE vaccine was approved, and routine vaccination was resumed in 2009 [11,12]. MHLW reports that the JE vaccination rate was approximately 80% between 1995 and 2004 [13]. More specifically, a report in 2008 showed that the percentage of Japanese who had a neutralizing antibody titer of 10 in JE [2]. 2.3. Vaccination and examination
2. Participants and methods
For measuring antibodies, serum was obtained from each subject before vaccination and 3e5 weeks after vaccination. Immunization history was determined by interviewing the subject or from the subject’s immunization record.
2.1. Participants
2.4. Statistical analysis
From October 2009 to March 2011, we recruited 113 Japanese who received JE vaccination at the National Center for Global Health and Medicine (NCGM), Tokyo, Japan. Neutralization
For differences in seroconversion rate (SCR) and geometric mean titer (GMT) of the neutralizing antibody, 95%-confidence intervals expressed as a 2-sided range were calculated for pre- and
Fig. 1. The JE-vaccination program of Japan. The primary vaccination is administrated twice at 1e4-week intervals between the ages of 6 and 90 months. The first booster vaccination is administered 1 year after the primary vaccination (1st step). The 2nd booster is administered between the ages of 9 and 13 years (2nd step), and the 3rd booster was administered during the ages of 14e15 years (3rd step).
240
N. Takeshita et al. / J Infect Chemother 20 (2014) 238e242
post-vaccination periods, and the 2 factors related this study, age and immunization history, were analyzed. For immunization history, we compared 3 groups: (1) persons with a history of JE vaccination and an immunization record (record group); (2) persons with a history of JE vaccination only (history group); and (3) persons who were not vaccinated with JE vaccine or could not confirm their vaccination history (unknown group). For age, we compared 25e39-years group and 40-years groups. Significance of differences in SCR was assessed using the Chi-square test, and significance of differences in GMT was assessed using the t test. A value of p < 0.05 was considered statistically significant. STATA Version 11 (Stata Corp LP, College Station, TX, USA) was used for all statistical analyses. This study was approved by the Institutional Review Board of the NCGM. (the Institutional Review Board of the NCGM number 689). 3. Results 3.1. Study participants’ dispositions and demographics The 79 study participants as a group were aged 40.7 9.4 years and included 54 males (68.4%); 13 (16.5%) participants were in the record group, 37 (46.8%) participants in the history group, and 29 (36.7%) in the unknown group (Table 1). In the record group, 8 participants had vaccinations 3 times, and the rest 2 times. Before vaccination, 38 (48.1%) participants were negative for the JE NT-Ab and 41 (51.9%) were positive for JE NT-Ab. Age was significantly different (p ¼ 0.02) between these groups: 42.8 8.5 years for the JE NT-Ab-negative group and 38.7 10.0 years for the JE NT-Ab-positive group. However, immunization history and frequency were not significantly different (Table 1). 3.2. Change in seroprotection rate (SPR) before and after vaccination The SPR was increased significantly by vaccination, going from 51.8% (n ¼ 41) before vaccination to 83.7% (n ¼ 74) after vaccination (Table 2). In the JE NT-Ab-negative group, 33 out of the 38 participants changed from negative to positive, an SCR of 86.8%. In the JE NT-Ab-positive group, antibody titers of 26 out of the 41 participants (63.4%) increased more than 4 fold after vaccination. For all participants, GMT increased from 14.7 to 70.1 after vaccination, and the geometric mean fold rise (GMFR) was 4.76 (Table 2). In the JE NT-Ab-negative group, 33 participants underwent seroconversion and 5 participants did not, but their ages, sex, immunization history, and frequency of past vaccination were not significantly different. Table 1 Characteristics of participants and JE immunization history. Characteristic
Age (mean SD) Male/Female Previous immunization recorda Previous immunization historyb (no record) Unknown record/history Previous JE-MB vaccine 3 doses 2 doses
Table 2 Effects of receiving inactivated Vero cell culture-derived Japanese encephalitis vaccine. Total (n ¼ 79) Pre-seroprotection rate (n) Post-seroprotection rate (n) Seroconversion rate (n) Pre-GMT (CI) Post-GMT (CI) GMFR (CI) Geometric titer 4-fold (%)
51.9% (41/79) 93.7% (74/79) 86.8% (33/38) 14.7 (10.9e19.9) 70.1 (47.6e103) 4.76 (3.76e6.06) 26/41 (63.4%)
3.3. Comparison of immunization history The record, history, and unknown groups had 13 (16.5%), 37 (46.8%), and 29 (36.7%) participants, respectively, and average ages for these groups were significantly different (p ¼ 0.00): 34.6 2.87 years for the record group, 39 1.19 years for the history group, 45.6 1.76 years for the unknown group. However, significant differences were not found in SPR before and after vaccination, SCR, GMT before and after vaccination, and GMFR (Table 3). 3.4. Comparison of age groups The GMT before vaccination was 14.7 (25e39 years, 22.0; 40 years, 10.5; p ¼ 0.02) and after vaccination was 70.1 (25e39 years, 129; 40 years, 42; p ¼ 0.01), being significantly higher in the 25e 39-years group than in the 40-years group. GMFR was 4.76 and again higher in the 25e39 years group, but the difference between groups was not statistically significant (25e39 years, 5.90; 40 years, 4.00; p ¼ 0.13). Moreover, 63.4% of the participants showed a 4-fold or greater increase in GMT from before to after vaccination, and although the rate was higher in the 25e39-years group, the difference between groups was not statistically significant (25e39 years, 73.9%; 40 years, 50.0%; p ¼ 0.12). The SCR was significantly different for the two groups (25e39 years, 69.2%; 40 years, 96.0%; p ¼ 0.04) (Table 4). 3.5. Participants with reliable immunization records For the 13 participants with confirmed vaccination records, the SPR was 53.8% before vaccination and 100% after vaccination, and the SCR was 100% (Table 3). For the 25e39-years group, the SPR was 63.9% before vaccination (history and unknown groups, 65.4%; record groups, 60.0%) and 88.9% after vaccination (history and unknown groups, 84.6%; record groups, 100%), and the SCR was 69.2% (history and unknown groups, 9 participants, 55.6%; record groups, 4 participants, 100%). 4. Discussion
Total (n ¼ 79)
JE NT-Abc negative (n ¼ 38)
JE NT-Ab positive (n ¼ 41)
p
40.7 9.4 54/25 13 37
42.8 8.5 27/11 6 19
38.7 10.0 27/14 7 18
0.02** 0.64* 1.00* 0.66*
29
13
16
0.82*
8 5
4 2
4 3
1.00* 1.00*
*The p-value was calculated using Fisher test. **The p-value was calculated using Manh-Whitney analysis. a Confirmed with documents. b Confirmed by history taking only. c JE NT-Ab ¼ Japanese encephalitis Neutralizing antibodies.
This study found that the mean age of the JE NT-Ab-negative group was 42.8 years, and SPR of the JE NT-Ab-positive group before vaccination was 63.9% for 25e39-years group and 41.9% for the 40-years group. These results are almost identical to those of JE surveillance in 2011 [17]. The immunity provided by vaccination can decrease with time. The random coefficient model suggests that the JE NT-Ab decreases by approximately 80%, changing to negative over 15 years [18], which means that other factors may be responsible for the higher SPR in the of elderly population than in the 40-years group; these factors may include differences in JEvaccination programs and the probability of natural infection in older people. Specifically, before 1966, more than 1000 cases of JE were reported in Japan [7,9], and from 1967 to 1974, a special JEvaccination program was conducted for children. During that time,
N. Takeshita et al. / J Infect Chemother 20 (2014) 238e242
241
Table 3 Seroprotection rates and geometric mean titers (GMT) in participants receiving inactivated Vero cell culture-derived Japanese encephalitis vaccine. Characteristic
Previous immunization record (n ¼ 13)
Previous immunization history only (n ¼ 37)
Unknown record/ history (n ¼ 29)
p
Age (mean, in years) Male/female Pre-seroprotection rate (n) Post-seroprotection rate (n) Seroconversion rate (n) Pre-GMT (CI) Post-GMT (CI) GMFR (CI) Geometric titer 4-fold % (CI)
34.6 2.87 8/5 53.8% (7/13) 100% (13/13) 100% (6/6) 19.0 (7.26e49.6) 151.4 (46.6e492) 8 (4.23e15.1) 71.4% (5/7)
39 1.19 23/14 48.6% (18/37) 83.8% (31/37) 78.9% (15/19) 14.8 (9.14e23.9) 60.2 (32.7e111) 4.08 (2.89e5.78) 66.7% (12/18)
45.6 1.76 23/6 55.2% (16/29) 96.6% (28/29) 92.3% (12/13) 13.0 (8.45e20.0) 60.0 (34.8e103) 4.63 (3.07e6.92) 56.3% (9/16)
0.00** 0.28* 0.86* 0.28* 0.32* 0.85** 0.31** 0.14** 0.73*
*The p-value was calculated using Chi-square test. **The p-value was calculated using KruskaleWallis analysis.
the recommended vaccination schedule was 2 doses with an interval of 7e10 days and a single booster dose just before the peak season; however, the booster varied regionally, every year in some areas, every 3e4 years in other areas [19,20]. This booster timing was one of the different points from regular vaccination program. After that vaccination program ended, a regular vaccination program was started. These reasons may account for the differences between the 25e39-years group and the 40-years group. The results of this study showed that most Japanese adults are protected effectively after one dose of Vero cell-derived JE vaccination. The efficacies of mouse brain-derived and Vero cell-derived JE vaccine were found to be similar for JE NT-Ab-negative adults [11]. Moreover, a single dose of Vero cell-derived JE vaccine (IxaaroÒ), which used aluminum hydroxide as the adjuvant, was effective in people who were previously vaccinated with inactivated mouse brain-derived JE vaccine [21,22]. Although immunization histories should be confirmed by documents, such confirmation was not possible in the case of many participants in this study, with records being available for only 16.5% of the participants. Because most people find it difficult to remember their immunization history from childhood, a public records system should be devised for maintaining JE immunization history accurately, as with other vaccinations. For the 13 participants with a definitive immunization history, SPR before vaccination was 53.8% and after vaccination was 100%, and the SCR was 100%. In this group, 10 participants were aged 20e39 years and 3 were aged 40 years. Although the number of participants with a definitive immunization history in this study was low, our findings suggest that one vaccination with the JE vaccine is adequately effective in this particular group. When comparing the two age groups, SPR before vaccination was significantly higher in the 25e 39-years group, whereas SPRs after vaccination with Vero cellderived vaccine were similar for the two groups. Accordingly, Table 4 Seroprotection rate and geometric mean titer of participants receiving JE vaccination. Variable
25e39 years old n ¼ 36)
40 years old (n ¼ 43)
p
Age (mean value in years) Male/female Pre-seroprotection rate Post-seroprotection rate Seroconversion rate Pre-GMT (CI) Post-GMT (CI) GMFR (CI) Geometric titer 4-fold
32.6 4.4 20/16 63.9% (23/36) 88.9% (32/36) 69.2% (9/13) 22.0 (13.1e37.1) 129 (67.3e249) 5.90 (3.97e8.69) 73.9% (17/23)
47.5 6.8 34/9 41.9% (18/43) 97.7% (42/43) 96.0% (24/25) 10.5 (7.52e14.7) 42.0 (27.7e63.6) 4.00 (2.99e5.35) 50.0% (9/18)
0.00** 0.02* 0.07* 0.17* 0.04* 0.02** 0.01** 0.13** 0.19*
*The p-value was calculated using Fisher test. **The p-value was calculated using Manh-Whitney analysis.
SCRs for the 25e39-years and 40-years groups were 69.2% and 96.0%, respectively, and the difference was statistically significant. The above results indicate that vaccination rates in people aged 25e39 years and the current prevalence of subclinical JE infection must be investigated. The 1st-step vaccination rate for JE virus reached approximately 80% by 2004 [13]. However, during 2005 and 2006, when JE vaccination was not recommended strongly, vaccination rates dropped to 22.1% and 4.0%, respectively, even for the 1st step [13]. Regular vaccination with Vero cell-derived JE vaccine has been recommended strongly since April 2010, but the additional vaccination rates for children aged 76 months (at the 1st step of 2primary vaccinations) were as low as 15.5% in 2009 and 30.6% in 2010, and the SPRs in these children in the future is anticipated to be lower than those recorded in previous surveys [23]. Currently, subclinical JE infection is considered to be widespread in Western Japan, where more cases of JE were reported previously, than in the eastern part of Japan, including Tokyo. However, surveys on JE antibodies conducted on children without vaccination history in West and East Japan found the same, approximately 10%, JE NTAb-positive rates in both areas [24]. In a 2008 survey of 3200 participants conducted in 11 prefectures of Japan, evaluation of unvaccinated participants showed that SPR was
