Vaccine 32 (2014) 996–1002
Contents lists available at ScienceDirect
Vaccine journal homepage: www.elsevier.com/locate/vaccine
The relationship between concentration of specific antibody at birth and subsequent response to primary immunization Christine Jones a,1,2 , Louisa Pollock b,1,3 , Sara M. Barnett a , Anna Battersby a,b , Beate Kampmann a,b,∗ a b
Academic Department of Paediatrics, Imperial College London, 2nd Floor Wright Fleming Building, Norfolk Place, London W2 1PG, UK4 Vaccinology Theme, Medical Research Council Unit – The Gambia, PO Box 273, Banjul, Gambia5
a r t i c l e
i n f o
Article history: Received 23 September 2013 Received in revised form 16 November 2013 Accepted 27 November 2013 Available online 14 December 2013 Keywords: Vaccine Infant Immune response
a b s t r a c t Background and aims: Trans-placentally acquired antibodies can protect infants from infection in the first months of life. However, high concentrations of antibody at birth may impact the infant’s own immune response to primary immunization. We examine the relationship between concentration of specific antibody to Bordetella pertussis, Haemophilus influenzae type b (Hib), tetanus toxoid and pneumococcal antigens at birth and following primary immunization. Methods: Healthy mother–infant pairs were recruited from a UK maternity unit. Peripheral blood samples were obtained at birth and 4 weeks after primary immunization. Specific antibody concentrations were determined using enzyme-linked immunosorbent assays. Pertussis antibody concentrations >50 IU/ml, Tetanus antibody levels >0.1 IU/ml and Hib antibody levels >0.15 mg/l were regarded as protective. Results: Following primary immunization, 35/36 (97%) infants had specific antibody concentrations associated with protection against Hib, 32/36 (89%) against pertussis and 36/36 (100%) against tetanus. Concentrations of all specific antibodies were significantly higher than at birth (p < 0.0001), except antitetanus toxoid, p = 0.41. However, there was an inverse correlation between infant antibody concentration at birth and fold-increase in antibody concentration post-immunization for tetanus: rs −0.86 (95%CI −0.93 to −0.74), p < 0.0001; pneumococcus: rs −0.82 (95% CI −0.91 to −0.67), p < 0.0001; pertussis: rs −0.77 (95% CI −0.89 to −0.58), p < 0.0001 and Hib: rs −0.66 (95%CI −0.82 to −0.42), p < 0.0001. The highest concentrations of specific IgG at birth were associated with lower concentrations post-immunization for tetanus (p = 0.009) and pneumococcus (p = 0.03). This association was not observed for Hib (p = 0.88) or pertussis (p = 0.14). Conclusion: Higher antibody concentration at birth appeared to inhibit the response to infant immunization for tetanus and pneumococcus; the effect was less marked for Hib and pertussis. However, the majority of infants achieved high antibody levels post-immunization. This supports maternal immunization, as high levels of maternally derived antibody at birth may not inhibit infants’ immunization responses in a clinically relevant manner. © 2014 Elsevier Ltd. All rights reserved.
∗ Corresponding author at: Academic Department of Paediatrics, Imperial College London, 2nd Floor Wright Fleming Building, Norfolk Place, London W2 1PG, UK. Tel.: +44 207 594 2063; fax: +44 207 594 3894. E-mail addresses: [email protected] (C. Jones), [email protected] (L. Pollock), [email protected] (S.M. Barnett), [email protected] (A. Battersby), [email protected] (B. Kampmann). 1 Joint first authors. 2 Present address: Paediatric Infectious Diseases Research Group, St George’s, University of London, Room 2.215, 2nd Floor Jenner Wing, London SW17 0RE, UK. Tel: +44 (0) 2087252788; fax: +44 (0) 2087250716. 3 Present address: Wellcome Trust Liverpool Glasgow Centre for Global Health Research, Block E, University of Liverpool, 70 Pembroke Place, Liverpool L69 3GF, UK. 4 Tel.: +44 207 594 2063; fax: +44 207 594 3894. 5 Tel.: +220 4495442/4495446x3001. 0264-410X/$ – see front matter © 2014 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.vaccine.2013.11.104
C. Jones et al. / Vaccine 32 (2014) 996–1002
1. Introduction Trans-placentally acquired antibodies help to protect infants from infection in the first few months of life, but also influence the development of the infant’s own immune response. The general principle that acquired maternal antibodies may inhibit the infant active immune response to primary immunization is well established. The effect is best characterized for live vaccines such as measles virus, where even minimal maternal antibody levels reduce vaccine response, with major implications for vaccination scheduling strategies worldwide [1,2]. While measles remains the paradigm, and the model for recent experimental work to determine the mechanism of this inhibitory effect [3], studies of other vaccines however have shown more varied results: for live vaccines, inhibitory effects have been demonstrated for oral poliovirus [4] and but not for mumps [5] or rubella [6]. Similarly, inhibitory effects of maternal antibodies on vaccine response have been shown for whole cell but not acellular pertussis vaccines [7–11]. Wang et al. recently demonstrated that even very high maternal concentrations of anti-HBs had no effect on the long-term immunogenicity of Hepatitis B vaccine [12]. The nature and extent of the inhibitory effect also varies in the literature. In summary, although multiple reasons for differences between studies can be found, it is clear that the existence or extent of an inhibitory effect cannot automatically be predicted for any new vaccine [13]. Since the majority of studies were undertaken over 20 years ago – several examining vaccines now obsolete – there is a need for new data to inform current and future vaccine strategies. This issue is particularly pertinent at a time when new maternal programmes are being implemented. Maternal pertussis immunization, for example, has become the major public health strategy to combat the rising number of pertussis cases seen in many countries recently [14,15]. We sought to determine the extent to which maternal antibody levels inhibit infant immune response to pertussis, Haemophilus Influenzae type B (Hib), tetanus and pneumoccocus immunization in a UK mother–infant cohort. These vaccine-preventable infections were selected for their relevance to maternal immunization approaches. The study was undertaken prior to the recent introduction of maternal pertussis immunization in the UK. In addition, we aimed to assess changes in maternal antibody levels post-partum, predicting that antibody levels would increase over time in the absence of any interventions.
2. Methods 2.1. Study population and study procedures The data presented in this manuscript were generated during follow-up of a wider mother–infant cohort study conducted at Imperial Healthcare NHS Trust, London, UK between March 2011 and January 2012 [16]. The study protocol and recruitment process has been previously described and the birth data presented [16]. All mothers provided written informed consent. Well, term infants with birth weight greater than 2500 g, born to well mothers, aged over 18 years, were recruited within 72 h of birth and followed up 1 month after completion of routine primary immunization. Paired blood samples were collected from mothers and infants around birth and at 5 months of post-natal age. Only infants with followup samples taken 4 weeks (±2 weeks) post-immunization were included for analysis. There was no significant correlation between the timing of the maternal follow-up sample and specific antibody concentration; therefore all maternal follow-up samples were included for analysis. Infants received the following vaccines in primary healthcare according the UK vaccination schedule during the
997
study period: Pediacel (DTaP/IPV/Hib) at 8, 12 and 16 weeks of postnatal age, Prevenar 13 at 8 and 16 weeks and either Menjugate or NeisVac-C (depending on supply) at 12 and 16 weeks. Infants also received BCG around birth as recommended in this residential area of London. Influenza is recommended during pregnancy, however was only received by 43% (25/61) of women in the study. Three women (3/61, 5%) received tetanus vaccination during pregnancy, of these infant follow-up data was available for two of the mother–infant pairs (2/36, 6%). 2.2. Laboratory assays Specific IgG to Bordetella pertussis antigens (pertussis toxin and filamentous hemagglutinin) was measured using SERION ELISA classic kits (ESR 120G, Serion Immundiagnostica GmbH, Würzburg, Germany). Limits of quantification for this assay were 10–1000 IU/ml. The antibody response measured is a collective response to two antigens. Although mixed pertussis antigen assays are not recommended for the diagnosis of pertussis due to low specificity, use in immunogenicity studies is accepted [17]. Specific IgG against tetanus toxoid was determined using SERION ELISA classic kits (ESR 108G). Limits of quantification of the assay were 0.05–5.00 IU/ml. Hib capsular polysaccharide specific IgG was measured using the VaccZymeTM Human Anti-Hib Enzyme Immunoassay kit (MK016, The Binding Site Ltd, Birmingham, England). Limits of quantification for the assay were 0.11–9.00 mg/dl. Pneumococcal Capsular Polysaccharide (PCP) specific IgG was measured using VaccZymeTM Anti-PCP Enzyme Immunoassay kits (MK012). Limits of quantification for the assay were 3.3–270.0 mg/dl. The pneumococcal assay included 23 polysaccharide antigens (covering 80% of virulent serotypes and 12 of the 13 serotypes included in Prevenar 13 pneumococcal conjugate vaccine) and incorporated C-polysaccharide antibody absorption. 2.3. Parameters used to assess infant vaccine response The geometric mean concentration of specific IgG postimmunization and the proportion of infants achieving “protective” specific antibody concentrations post-immunization were determined. Anti-tetanus IgG concentrations were regarded as protective if >0.1 IU/ml, in accordance with international guidelines [18]. Anti-Hib IgG concentrations of >0.15 mg/l and >1.0 mg/l have been correlated with minimum and long-term protective immunity respectively. Analysis was made at the minimum threshold for the infants, in line with reported literature. Analysis was carried out at the higher threshold for the mothers [19,20]. There is no established correlate of protection for pertussis; however, low antibody concentrations are highly correlated with susceptibility to infection [21–24]. It is established in the literature that a ‘positive’ or detectable response in this diagnostic test may be consistent with some measure of protection [25]. A positive response in this assay of >50 IU/ml was therefore interpreted as potentially protective in this context. No level of protective immunity has been established for a collective response to multiple pneumococcal serotypes. A threshold value was therefore not used. 2.4. Parameters used to examine the relationship between infant antibody levels at birth and response to immunization The relative antibody response to immunization was determined by the fold increase in specific antibody concentration between birth and 4 weeks post-immunization. The absolute antibody response to immunization was defined as the geometric mean concentration (GMC) of specific antibody post-immunization compared to the concentration at birth. Finally, as the relationship
998
C. Jones et al. / Vaccine 32 (2014) 996–1002
Fig. 1. Participant flow diagram.
between infant antibody concentration at birth and vaccine response may not be linear, we grouped infants according to specific antibody concentration at birth. Using data from the study population, infants were categorized into three centile ranges: infants with specific IgG concentration less than the 25th centile at birth, between the 25th and 75th centile, and above the 75th centile. Other authors have categorized using arbitrary cut-offs [9], but we believe the use of centile ranges based on our study population makes fewer assumptions about “high” and “low” concentrations in the absence of published validated reference data. The concentration of specific IgG post-immunization was compared between each group. 2.5. Data management and statistical analysis Where assay results were below the lower limit of quantification defined by the manufacturer an arbitrary value of half the lower limit of detection was assigned. For assay results above the upper limit of quantification samples were re-tested with serial dilutions until a measurable value was obtained. Statistical analyses were completed using IBM SPSS version 20 (SPSS Inc, Chicago, Illinois) and GraphPad Prism version 5.04 (GraphPad Software Inc, La Jolla, California). Two-sided p < 0.05 was considered significant. Comparisons at different time points were made using the Mann Whitney U test for independent samples, or Wilcoxon matched pairs test for paired samples. Spearman’s correlation co-efficient was used for tests of correlation. The Kruskal–Wallis test was used to compare the three sets of infants grouped according to centiles. 3. Results 3.1. Study population The number of subjects included at each stage of the study is summarized in Fig. 1. Characteristics of the cohort at recruitment and reasons for non-participation have been described
previously [16]. The overall study cohort included a small subgroup of HIV-infected mothers; this sub-group is not included in this follow-up study as it was of insufficient size to allow meaningful comparison. All infants attending follow-up were vaccinated at 2, 3 and 4 months according to the UK schedule at the time of the study and received 3 doses of Diphtheria/Tetanus/acellular Pertussis/inactivated Polio/Hib vaccine, 3 doses of 13 valent pneumococcal conjugate vaccine and 2 doses of Meningococcus C vaccine. In addition 35 of the 36 infants had received BCG vaccination at birth. Characteristics of subjects included for infant and maternal analysis are shown in Table 1. There were 61 mother–infant pairs who attended for follow-up within the study period, however only 36 mother–infant pairs attended within the specific window of 4 weeks (±2 weeks) of completion of primary immunization. Compared to those mother–infant pairs who defaulted or were excluded, a significantly greater proportion of the infants included for analysis at follow-up were female and were born by caesarean section, otherwise there were no significant differences in clinical characteristics between these groups (Supplementary online Table S1). Supplementary material related to this article can be found, in the online version, at http://dx.doi.org/10.1016/j.vaccine. 2013.11.104.
3.2. Infant response to immunization GMC of specific IgG at birth and post-immunization was compared. At 4 weeks post-immunization, infant antibody concentrations to Hib, pertussis, and pneumococcus had significantly increased (Table 2). Tetanus antibody concentrations, however, were not significantly different (Table 2). After completion of primary immunization, the majority of infants had specific antibody concentrations associated with protection against Hib, 35/36 (97%) and tetanus 36/36 (100%) and a potentially protective response to pertussis antigens 32/36 (89%).
C. Jones et al. / Vaccine 32 (2014) 996–1002
999
Table 1 Characteristics of subjects. Subject characteristics
Participants included in analysis of infant samples no. (%) n = 36
Participants included in analysis of maternal samples no. (%) n = 61
Maternal age, mean (95%CI) Maternal ethnicity Asian or Asian British Black or Black British White British Other White background Mixed or other ethnic background Gestation, median (IQR) in weeks Female infant sex Infant delivered by caesarean section Birth weight, mean (95% CI) in kg Breast-feeding at birth Breast-feeding at follow-up
32.2 (30.1–34.2)
32.7 (31.2–34.2)
2 (6%) 10 (28%) 8 (22%) 7 (19%) 9 (25%) 40 (38–41) 12 (33%) 19 (53%) 3.3 (3.2–3.5) 26 (72%) 12 (33%)
5 (8%) 16 (26%) 13 (21%) 14 (23%) 13 (21%) 40 (39–41) 28 (46%) 26 (43%) 3.4 (3.3–3.5) 42 (69%) 20 (33%)
Table 2 Maternal and infant geometric mean concentration of specific IgG. Geometric mean concentration of specific IgG (95%CI)
Hib (mg/L) Pertussis (FDA U/ml) Pneumococcus (mg/L) Tetanus (IU/ml)
Infants at birth
Infants at 5 months
p
Mothers at birth
Mothers at 5 months
p
0.6 (0.4–1.0) 28.6 (21.0–39.0) 46.8 (34.8–63.0) 0.6 (0.3–1.0)
3.0 (1.7–5.3) 133.9 (97.5–184.1) 103.0 (82.0–129.6) 1.2 (0.9–1.7)
Contents lists available at ScienceDirect
Vaccine journal homepage: www.elsevier.com/locate/vaccine
The relationship between concentration of specific antibody at birth and subsequent response to primary immunization Christine Jones a,1,2 , Louisa Pollock b,1,3 , Sara M. Barnett a , Anna Battersby a,b , Beate Kampmann a,b,∗ a b
Academic Department of Paediatrics, Imperial College London, 2nd Floor Wright Fleming Building, Norfolk Place, London W2 1PG, UK4 Vaccinology Theme, Medical Research Council Unit – The Gambia, PO Box 273, Banjul, Gambia5
a r t i c l e
i n f o
Article history: Received 23 September 2013 Received in revised form 16 November 2013 Accepted 27 November 2013 Available online 14 December 2013 Keywords: Vaccine Infant Immune response
a b s t r a c t Background and aims: Trans-placentally acquired antibodies can protect infants from infection in the first months of life. However, high concentrations of antibody at birth may impact the infant’s own immune response to primary immunization. We examine the relationship between concentration of specific antibody to Bordetella pertussis, Haemophilus influenzae type b (Hib), tetanus toxoid and pneumococcal antigens at birth and following primary immunization. Methods: Healthy mother–infant pairs were recruited from a UK maternity unit. Peripheral blood samples were obtained at birth and 4 weeks after primary immunization. Specific antibody concentrations were determined using enzyme-linked immunosorbent assays. Pertussis antibody concentrations >50 IU/ml, Tetanus antibody levels >0.1 IU/ml and Hib antibody levels >0.15 mg/l were regarded as protective. Results: Following primary immunization, 35/36 (97%) infants had specific antibody concentrations associated with protection against Hib, 32/36 (89%) against pertussis and 36/36 (100%) against tetanus. Concentrations of all specific antibodies were significantly higher than at birth (p < 0.0001), except antitetanus toxoid, p = 0.41. However, there was an inverse correlation between infant antibody concentration at birth and fold-increase in antibody concentration post-immunization for tetanus: rs −0.86 (95%CI −0.93 to −0.74), p < 0.0001; pneumococcus: rs −0.82 (95% CI −0.91 to −0.67), p < 0.0001; pertussis: rs −0.77 (95% CI −0.89 to −0.58), p < 0.0001 and Hib: rs −0.66 (95%CI −0.82 to −0.42), p < 0.0001. The highest concentrations of specific IgG at birth were associated with lower concentrations post-immunization for tetanus (p = 0.009) and pneumococcus (p = 0.03). This association was not observed for Hib (p = 0.88) or pertussis (p = 0.14). Conclusion: Higher antibody concentration at birth appeared to inhibit the response to infant immunization for tetanus and pneumococcus; the effect was less marked for Hib and pertussis. However, the majority of infants achieved high antibody levels post-immunization. This supports maternal immunization, as high levels of maternally derived antibody at birth may not inhibit infants’ immunization responses in a clinically relevant manner. © 2014 Elsevier Ltd. All rights reserved.
∗ Corresponding author at: Academic Department of Paediatrics, Imperial College London, 2nd Floor Wright Fleming Building, Norfolk Place, London W2 1PG, UK. Tel.: +44 207 594 2063; fax: +44 207 594 3894. E-mail addresses: [email protected] (C. Jones), [email protected] (L. Pollock), [email protected] (S.M. Barnett), [email protected] (A. Battersby), [email protected] (B. Kampmann). 1 Joint first authors. 2 Present address: Paediatric Infectious Diseases Research Group, St George’s, University of London, Room 2.215, 2nd Floor Jenner Wing, London SW17 0RE, UK. Tel: +44 (0) 2087252788; fax: +44 (0) 2087250716. 3 Present address: Wellcome Trust Liverpool Glasgow Centre for Global Health Research, Block E, University of Liverpool, 70 Pembroke Place, Liverpool L69 3GF, UK. 4 Tel.: +44 207 594 2063; fax: +44 207 594 3894. 5 Tel.: +220 4495442/4495446x3001. 0264-410X/$ – see front matter © 2014 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.vaccine.2013.11.104
C. Jones et al. / Vaccine 32 (2014) 996–1002
1. Introduction Trans-placentally acquired antibodies help to protect infants from infection in the first few months of life, but also influence the development of the infant’s own immune response. The general principle that acquired maternal antibodies may inhibit the infant active immune response to primary immunization is well established. The effect is best characterized for live vaccines such as measles virus, where even minimal maternal antibody levels reduce vaccine response, with major implications for vaccination scheduling strategies worldwide [1,2]. While measles remains the paradigm, and the model for recent experimental work to determine the mechanism of this inhibitory effect [3], studies of other vaccines however have shown more varied results: for live vaccines, inhibitory effects have been demonstrated for oral poliovirus [4] and but not for mumps [5] or rubella [6]. Similarly, inhibitory effects of maternal antibodies on vaccine response have been shown for whole cell but not acellular pertussis vaccines [7–11]. Wang et al. recently demonstrated that even very high maternal concentrations of anti-HBs had no effect on the long-term immunogenicity of Hepatitis B vaccine [12]. The nature and extent of the inhibitory effect also varies in the literature. In summary, although multiple reasons for differences between studies can be found, it is clear that the existence or extent of an inhibitory effect cannot automatically be predicted for any new vaccine [13]. Since the majority of studies were undertaken over 20 years ago – several examining vaccines now obsolete – there is a need for new data to inform current and future vaccine strategies. This issue is particularly pertinent at a time when new maternal programmes are being implemented. Maternal pertussis immunization, for example, has become the major public health strategy to combat the rising number of pertussis cases seen in many countries recently [14,15]. We sought to determine the extent to which maternal antibody levels inhibit infant immune response to pertussis, Haemophilus Influenzae type B (Hib), tetanus and pneumoccocus immunization in a UK mother–infant cohort. These vaccine-preventable infections were selected for their relevance to maternal immunization approaches. The study was undertaken prior to the recent introduction of maternal pertussis immunization in the UK. In addition, we aimed to assess changes in maternal antibody levels post-partum, predicting that antibody levels would increase over time in the absence of any interventions.
2. Methods 2.1. Study population and study procedures The data presented in this manuscript were generated during follow-up of a wider mother–infant cohort study conducted at Imperial Healthcare NHS Trust, London, UK between March 2011 and January 2012 [16]. The study protocol and recruitment process has been previously described and the birth data presented [16]. All mothers provided written informed consent. Well, term infants with birth weight greater than 2500 g, born to well mothers, aged over 18 years, were recruited within 72 h of birth and followed up 1 month after completion of routine primary immunization. Paired blood samples were collected from mothers and infants around birth and at 5 months of post-natal age. Only infants with followup samples taken 4 weeks (±2 weeks) post-immunization were included for analysis. There was no significant correlation between the timing of the maternal follow-up sample and specific antibody concentration; therefore all maternal follow-up samples were included for analysis. Infants received the following vaccines in primary healthcare according the UK vaccination schedule during the
997
study period: Pediacel (DTaP/IPV/Hib) at 8, 12 and 16 weeks of postnatal age, Prevenar 13 at 8 and 16 weeks and either Menjugate or NeisVac-C (depending on supply) at 12 and 16 weeks. Infants also received BCG around birth as recommended in this residential area of London. Influenza is recommended during pregnancy, however was only received by 43% (25/61) of women in the study. Three women (3/61, 5%) received tetanus vaccination during pregnancy, of these infant follow-up data was available for two of the mother–infant pairs (2/36, 6%). 2.2. Laboratory assays Specific IgG to Bordetella pertussis antigens (pertussis toxin and filamentous hemagglutinin) was measured using SERION ELISA classic kits (ESR 120G, Serion Immundiagnostica GmbH, Würzburg, Germany). Limits of quantification for this assay were 10–1000 IU/ml. The antibody response measured is a collective response to two antigens. Although mixed pertussis antigen assays are not recommended for the diagnosis of pertussis due to low specificity, use in immunogenicity studies is accepted [17]. Specific IgG against tetanus toxoid was determined using SERION ELISA classic kits (ESR 108G). Limits of quantification of the assay were 0.05–5.00 IU/ml. Hib capsular polysaccharide specific IgG was measured using the VaccZymeTM Human Anti-Hib Enzyme Immunoassay kit (MK016, The Binding Site Ltd, Birmingham, England). Limits of quantification for the assay were 0.11–9.00 mg/dl. Pneumococcal Capsular Polysaccharide (PCP) specific IgG was measured using VaccZymeTM Anti-PCP Enzyme Immunoassay kits (MK012). Limits of quantification for the assay were 3.3–270.0 mg/dl. The pneumococcal assay included 23 polysaccharide antigens (covering 80% of virulent serotypes and 12 of the 13 serotypes included in Prevenar 13 pneumococcal conjugate vaccine) and incorporated C-polysaccharide antibody absorption. 2.3. Parameters used to assess infant vaccine response The geometric mean concentration of specific IgG postimmunization and the proportion of infants achieving “protective” specific antibody concentrations post-immunization were determined. Anti-tetanus IgG concentrations were regarded as protective if >0.1 IU/ml, in accordance with international guidelines [18]. Anti-Hib IgG concentrations of >0.15 mg/l and >1.0 mg/l have been correlated with minimum and long-term protective immunity respectively. Analysis was made at the minimum threshold for the infants, in line with reported literature. Analysis was carried out at the higher threshold for the mothers [19,20]. There is no established correlate of protection for pertussis; however, low antibody concentrations are highly correlated with susceptibility to infection [21–24]. It is established in the literature that a ‘positive’ or detectable response in this diagnostic test may be consistent with some measure of protection [25]. A positive response in this assay of >50 IU/ml was therefore interpreted as potentially protective in this context. No level of protective immunity has been established for a collective response to multiple pneumococcal serotypes. A threshold value was therefore not used. 2.4. Parameters used to examine the relationship between infant antibody levels at birth and response to immunization The relative antibody response to immunization was determined by the fold increase in specific antibody concentration between birth and 4 weeks post-immunization. The absolute antibody response to immunization was defined as the geometric mean concentration (GMC) of specific antibody post-immunization compared to the concentration at birth. Finally, as the relationship
998
C. Jones et al. / Vaccine 32 (2014) 996–1002
Fig. 1. Participant flow diagram.
between infant antibody concentration at birth and vaccine response may not be linear, we grouped infants according to specific antibody concentration at birth. Using data from the study population, infants were categorized into three centile ranges: infants with specific IgG concentration less than the 25th centile at birth, between the 25th and 75th centile, and above the 75th centile. Other authors have categorized using arbitrary cut-offs [9], but we believe the use of centile ranges based on our study population makes fewer assumptions about “high” and “low” concentrations in the absence of published validated reference data. The concentration of specific IgG post-immunization was compared between each group. 2.5. Data management and statistical analysis Where assay results were below the lower limit of quantification defined by the manufacturer an arbitrary value of half the lower limit of detection was assigned. For assay results above the upper limit of quantification samples were re-tested with serial dilutions until a measurable value was obtained. Statistical analyses were completed using IBM SPSS version 20 (SPSS Inc, Chicago, Illinois) and GraphPad Prism version 5.04 (GraphPad Software Inc, La Jolla, California). Two-sided p < 0.05 was considered significant. Comparisons at different time points were made using the Mann Whitney U test for independent samples, or Wilcoxon matched pairs test for paired samples. Spearman’s correlation co-efficient was used for tests of correlation. The Kruskal–Wallis test was used to compare the three sets of infants grouped according to centiles. 3. Results 3.1. Study population The number of subjects included at each stage of the study is summarized in Fig. 1. Characteristics of the cohort at recruitment and reasons for non-participation have been described
previously [16]. The overall study cohort included a small subgroup of HIV-infected mothers; this sub-group is not included in this follow-up study as it was of insufficient size to allow meaningful comparison. All infants attending follow-up were vaccinated at 2, 3 and 4 months according to the UK schedule at the time of the study and received 3 doses of Diphtheria/Tetanus/acellular Pertussis/inactivated Polio/Hib vaccine, 3 doses of 13 valent pneumococcal conjugate vaccine and 2 doses of Meningococcus C vaccine. In addition 35 of the 36 infants had received BCG vaccination at birth. Characteristics of subjects included for infant and maternal analysis are shown in Table 1. There were 61 mother–infant pairs who attended for follow-up within the study period, however only 36 mother–infant pairs attended within the specific window of 4 weeks (±2 weeks) of completion of primary immunization. Compared to those mother–infant pairs who defaulted or were excluded, a significantly greater proportion of the infants included for analysis at follow-up were female and were born by caesarean section, otherwise there were no significant differences in clinical characteristics between these groups (Supplementary online Table S1). Supplementary material related to this article can be found, in the online version, at http://dx.doi.org/10.1016/j.vaccine. 2013.11.104.
3.2. Infant response to immunization GMC of specific IgG at birth and post-immunization was compared. At 4 weeks post-immunization, infant antibody concentrations to Hib, pertussis, and pneumococcus had significantly increased (Table 2). Tetanus antibody concentrations, however, were not significantly different (Table 2). After completion of primary immunization, the majority of infants had specific antibody concentrations associated with protection against Hib, 35/36 (97%) and tetanus 36/36 (100%) and a potentially protective response to pertussis antigens 32/36 (89%).
C. Jones et al. / Vaccine 32 (2014) 996–1002
999
Table 1 Characteristics of subjects. Subject characteristics
Participants included in analysis of infant samples no. (%) n = 36
Participants included in analysis of maternal samples no. (%) n = 61
Maternal age, mean (95%CI) Maternal ethnicity Asian or Asian British Black or Black British White British Other White background Mixed or other ethnic background Gestation, median (IQR) in weeks Female infant sex Infant delivered by caesarean section Birth weight, mean (95% CI) in kg Breast-feeding at birth Breast-feeding at follow-up
32.2 (30.1–34.2)
32.7 (31.2–34.2)
2 (6%) 10 (28%) 8 (22%) 7 (19%) 9 (25%) 40 (38–41) 12 (33%) 19 (53%) 3.3 (3.2–3.5) 26 (72%) 12 (33%)
5 (8%) 16 (26%) 13 (21%) 14 (23%) 13 (21%) 40 (39–41) 28 (46%) 26 (43%) 3.4 (3.3–3.5) 42 (69%) 20 (33%)
Table 2 Maternal and infant geometric mean concentration of specific IgG. Geometric mean concentration of specific IgG (95%CI)
Hib (mg/L) Pertussis (FDA U/ml) Pneumococcus (mg/L) Tetanus (IU/ml)
Infants at birth
Infants at 5 months
p
Mothers at birth
Mothers at 5 months
p
0.6 (0.4–1.0) 28.6 (21.0–39.0) 46.8 (34.8–63.0) 0.6 (0.3–1.0)
3.0 (1.7–5.3) 133.9 (97.5–184.1) 103.0 (82.0–129.6) 1.2 (0.9–1.7)
