Conjugate vaccine technology using covalent coupling of bacterial capsular polysaccharides to a carrier protein circumvents the relatively immature B-cell responses of infants when exposed to capsular polysaccharide, by activating T-helper cells.1 Conjugate vaccines are highly effective in the prevention of disease in children due to encapsulated organisms such as Haemophilus influenzae type b (Hib),2,3Neisseria meningitidis,4 and Streptococcus pneumoniae.5
A 10-valent pneumococcal conjugate vaccine (PHiD-CV, GlaxoSmithKline [GSK] Biologicals, Rixensart, Belgium), using a recombinant form of protein D (the 42 kD nonlipidated form of a highly conserved cell-surface lipoprotein of non-typeable H. influenzae [NTHi]) as carrier protein for 8 out of the 10 vaccine serotypes, has the potential to offer protection against both pneumococcal and NTHi diseases. The PHiD-CV vaccine contains serotypes 1, 5, and 7F in addition to the 7 pneumococcal serotypes (4, 6B, 9V, 14, 18C, 19F, 23F) present in the currently licensed 7-valent pneumococcal conjugate vaccine (7vCRM). PHiD-CV was shown to be immunogenic and well tolerated when coadministered with DTPa-based combination vaccines for the primary and booster vaccinations of infants.6–8
Despite the increasing use of acellular pertussis vaccines (DTPa), whole cell pertussis preparations (DTPw) are still widely used. In 2005, 85 of 87 developing countries continued to use DTPw vaccines in their vaccination programs.9 Since 2006, the GAVI Alliance has supported introduction of pneumococcal conjugate vaccine in GAVI fund-eligible countries within the developing world. The World Health Organization (WHO) subsequently recommended the introduction of pneumococcal conjugate vaccines into the developing world.10 Thus specific studies that evaluate immunogenicity and safety of conjugate pneumococcal vaccines when coadministered with DTPw-based combination vaccines are needed.
The PHiD-CV vaccine is intended for use in both industrialized and developing countries, thereby encompassing a range of primary vaccination schedules and coadministrations with other pediatric vaccines. This study evaluated immunogenicity of the PHiD-CV vaccine in 2 countries using 2 different primary vaccination schedules. Children in the Philippines received primary vaccination in the accelerated 6-, 10-, and 14-week schedule endorsed by the WHO Expanded Program on Immunization.11 Children in Poland received as primary vaccination the 2-, 4-, and 6-month schedule used by many countries globally. In both countries, the PHiD-CV vaccine was coadministered with a combined DTPw-hepatitis B-Hib (DTPw-HBV/Hib) vaccine and with either injectable inactivated (IPV, Poland) or oral live attenuated (OPV, the Philippines) poliovirus vaccines.
Immune responses after primary immunization with both pneumococcal conjugate vaccines are reported in this publication. The immune response to the coadministered vaccines (DTPw-HBV/Hib, OPV and IPV) and the safety and reactogenicity data are reported elsewhere.8,12 A study to assess booster vaccination outcomes during the second year of life is currently ongoing and will be reported separately.
The study was randomized, controlled, and double-blind (107007/NCT00344318) and conducted between 7 August 2006 and 27 April 2007. Subjects were enrolled from 1 center in the Philippines and from 6 centers in Poland. In each country, eligible infants were randomized (3:1 ratio) to receive primary vaccination with either PHiD-CV or the licensed 7vCRM vaccine as indicated in Table 1. Due to the different appearance of the PHiD-CV and 7vCRM vaccines, an observer blind procedure (ie, vaccines were administered by a different person than the one who performed the safety assessments) was followed to keep the study double-blind.
The study was conducted according to Good Clinical Practice guidelines and the Declaration of Helsinki (Somerset West, 1996 version). The study protocol was approved by ethics review committees of participating centers. Written informed consent was obtained from the parents/guardian of each subject before enrolment.
Study subjects were healthy infants between 6 and 12 weeks of age, born after a gestation period between 36 and 42 weeks. Infants were excluded from participation if they had received previous vaccination against diphtheria, tetanus, pertussis, polio, hepatitis B, Hib and/or S. pneumoniae, with the exception of HBV given within the first 2 weeks of life. Infants were also excluded if they had a history of diphtheria, tetanus, pertussis, hepatitis B, polio, or Hib disease. Other exclusion criteria included a history of allergic disease or reactions likely to be exacerbated by any component of the study vaccines, a history of seizures or neurologic disease, suspected or confirmed immunosuppressive condition or a family history of immunodeficiency, receipt of immunosuppressive therapy, the presence of major congenital defects or serious chronic illness, or receipt (or planned receipt) of immunoglobulin or blood products since birth.
The PHiD-CV vaccine contained 1 μg of each capsular polysaccharide of the pneumococcal serotypes 1, 5, 6B, 7F, 9V, 14 and 23F, and 3 μg of serotype 4, conjugated individually to protein D; 3 μg of serotype 18C capsular polysaccharide conjugated to tetanus toxoid; and 3 μg of serotype 19F capsular polysaccharide conjugated to diphtheria toxoid. The composition of the commercially available DTPw-HBV/Hib vaccine (Tritanrix™ HepB/Hib) vaccine has been described previously.13 OPV (Polio Sabin™) contained 106 TCID50 poliovirus type 1, 105 TCID50 poliovirus type 2, and 105.5 TCID50 poliovirus type 3. IPV (Poliorix™) contained 40D units of inactivated poliovirus type 1 (Mahoney), 8D units of poliovirus type 2 (MEF-1), and 32D units of poliovirus type 3 (Saukett). PHiD-CV, DTPw-HBV/Hib, OPV, and IPV vaccines were manufactured by GlaxoSmithKline Biologicals, Rixensart.
The commercially available control vaccine, 7vCRM (Prevenar™/Prevnar™; Wyeth Lederle, Philadelphia, PA, USA) comprised 4 μg of serotype 6B capsular polysaccharide and 2 μg of capsular polysaccharide for serotypes 4, 9V, 14, 18C, 19F, and 23F conjugated to CRM197. PHiD-CV or 7vCRM vaccines were administered intramuscularly into the right thigh. DTPw-HBV/Hib and IPV vaccines were administered intramuscularly into the left thigh.
All safety and reactogenicity data (including the primary objective of this study) are reported elsewhere.8
Two blood samples were collected from all subjects: before the first vaccine dose and 1 month after completion of primary vaccination. Sera were analyzed in a blinded manner using validated methods at GSK Biologicals’ laboratories.
Serum anti-pneumococcal IgG concentrations were measured in all subjects by GSK's 22F-inhibition enzyme-linked immunosorbent assay (ELISA) as previously described.14,15 The assay cut-off was 0.05 μg/mL. A reference antibody concentration of 0.2 μg/mL using GSK's ELISA, equivalent to 0.35 μg/mL when using the non-22F ELISA method at the WHO reference laboratory15,16 was used to analyze immune responses. The 0.35μg/mL threshold with GSK's 22F-ELISA assay (corresponding to a threshold of approximately 0.5 μg/mL when using the WHO reference laboratory ELISA), was also evaluated.
OPA was measured in a randomly selected subset of 200 subjects from each country, by a killing assay using a HL60 cell line.17 The results were presented as the dilution of serum (opsonic titer) able to sustain 50% killing of live pneumococci under the assay conditions. The threshold of the assay was set at an opsonic titer of 8,18 which was shown to correlate to protection against IPD.14 IgG antibodies to NTHi protein D were measured in all subjects, by an in-house ELISA. The assay cut-off was 100 EL.U/mL.
The immunogenicity analysis was performed on the according to protocol (ATP) cohort.
Seropositivity rates with exact 95% CIs were calculated for all vaccine pneumococcal serotypes, cross-reactive serotypes 6A and 19A and for protein D. Antibody geometric mean concentrations (GMCs) and OPA geometric mean titers (GMTs) were calculated with 95% CIs by taking the antilog of the mean of the log concentration/titer transformations. Antibody concentrations/OPA titers below the assay cut-off were given an arbitrary value of half the cut-off for the purpose of GMC/GMT calculation.
A total of 761 enrolled and vaccinated subjects (380 in the Philippines and 381 in Poland) were included in the ATP immunogenicity cohort (Table 1). Overall, 570 subjects in the ATP immunogenicity cohort received primary vaccination with PHiD-CV and 191 with 7vCRM. In each country, no major differences were observed between the PHiD-CV and 7vCRM groups regarding demographic characteristics of the ATP cohort for immunogenicity (Table 1).
Immunogenicity: 6-, 10-, and 14-Week Schedule in the Philippines
After primary vaccination in Filipino infants at 6, 10, and 14 weeks of age, the percentage of subjects with antibody concentrations ≥0.2 μg/mL, and with antibody concentrations ≥0.35 μg/mL, was within the same range in the PHiD-CV and 7vCRM groups for all 7 pneumococcal serotypes common to both vaccines (Tables 2, 3). One month after the third vaccine dose, at least 99.6% of PHiD-CV-primed subjects had antibody concentrations ≥0.2 μg/mL against vaccine pneumococcal serotypes 1, 5, and 7F. Post-primary vaccination antibody GMCs against serotypes 18C and 19F were significantly higher in the PHiD-CV group compared with the 7vCRM group (no overlap of 95% CIs; Table 2, Fig. 1). For all the other pneumococcal serotypes common to both vaccines, antibody GMCs were within the same range between groups.
One month after primary vaccination at 6, 10, and 14 weeks of age, the percentage of subjects with OPA titers ≥8 was within the same range in the PHiD-CV and 7vCRM groups for all 7 common vaccine serotypes (Table 4), although the percentage of subjects with OPA titers ≥8, tended to be higher for serotype 19F in the PHiD-CV group. In PHiD-CV recipients, OPA titers ≥8 were observed in at least 99.3% of subjects against the PHiD-CV vaccine pneumococcal serotypes 5 and 7F, and in 82.4% of the subjects against serotype 1. This compared with OPA titers ≥8 in fewer than 25% of 7vCRM-primed subjects for these 3 serotypes. The post-primary OPA GMTs were significantly higher in the PHiD-CV group for serotypes 18C and 19F, whereas the OPA GMT for serotype 23F was significantly higher in the 7vCRM group (Table 4, Fig. 1).
The primary vaccination with PHiD-CV induced a measurable immune response against cross-reactive serotypes 6A and 19A. The percentage of subjects with anti-pneumococcal serotype 19A antibodies ≥0.2 or ≥0.35 μg/mL and the anti-19A antibody GMCs were significantly higher in the PHiD-CV group than the 7vCRM group. The percentage of subjects with OPA titers ≥8 and the OPA GMT were significantly higher in the PHiD-CV group for serotype 19A (Table 4).
One month after primary vaccination, all PHiD-CV-primed subjects had measurable antibodies against protein D (Table 5). The anti-protein D antibody GMC was 36-fold higher in the PHiD-CV group compared with the 7vCRM group.
Immunogenicity: 2-, 4-, and 6-Month Schedule in Poland
After primary vaccination of Polish infants at 2, 4, and 6 months of age, the percentage of subjects with antibody concentrations ≥0.2 μg/mL was within the same range in the PHiD-CV and 7vCRM groups for 5 of the 7 pneumococcal serotypes common to both vaccines (Table 2). The percentage of subjects reaching the 0.2 μg/mL threshold tended to be lower for serotypes 6B and 23F in PHiD-CV vaccinees. Similar results were observed using the ≥0.35 μg/mL threshold, with fewer PHiD-CV vaccinees achieving this threshold for serotypes 6B and 23F (Table 3). One month after the third vaccine dose, at least 98.2% of PHiD-CV-primed subjects had antibody concentrations ≥0.2 μg/mL against vaccine pneumococcal serotypes 1, 5, and 7F.
Post-primary vaccination, antibody GMCs against serotypes 18C and 19F were significantly higher in the PHiD-CV group compared with the 7vCRM group (Table 2, Fig. 1). Antibody GMCs against the other pneumococcal serotypes common to both vaccines were significantly lower in the PHiD-CV group compared with the 7vCRM group.
One month after primary vaccination, the percentage of subjects with OPA titers ≥8 was within the same range in the PHiD-CV and 7vCRM groups for most common serotypes (Table 4). The percentage of subjects with OPA titers ≥8, tended to be higher for serotype 19F and lower for serotype 23F in the PHiD-CV group. In PHiD-CV recipients, OPA titers ≥8 were observed in at least 88.2% of subjects against the PHiD-CV vaccine pneumococcal serotypes 5 and 7F, and in 43.1% of subjects against serotype 1. This compared with OPA titers ≥8 in fewer than 11% of 7vCRM-primed subjects for these 3 serotypes. The post-primary OPA GMTs against serotype 19F was significantly higher in the PHiD-CV group, whereas the OPA GMT for serotype 23F was significantly higher in the 7vCRM group (Table 4, Fig. 1).
The primary vaccination with PHiD-CV induced a measurable immune response against cross-reactive serotypes 6A and 19A. The percentage of subjects with anti-pneumococcal serotype 19A antibodies ≥0.2 μg/mL or ≥0.35μg/mL (Tables 2, 3) and anti-19A antibody GMCs (Table 4) were significantly higher in the PHiD-CV group than the 7vCRM group. The percentage of subjects with OPA titers ≥8 and OPA GMTs tended to be lower for serotype 6A in the PHiD-CV group.
One month after primary vaccination all PHiD-CV-primed subjects had measurable antibodies against protein D (Table 5). The anti-protein D antibody GMC was 30-fold higher in the PHiD-CV group compared with the 7vCRM group.
For most of the serotypes common to both vaccines and for both schedules, the immunogenicity profile of the PHiD-CV vaccine was in line with that of the 7vCRM control vaccine in terms of the percentage of subjects who reached the 0.2 μg/mL threshold for anti-pneumococcal antibodies and in terms of the percentage of subjects with OPA titers ≥8 after primary vaccination. Some differences between both vaccines and both schedules were, however, noted. In the Philippines, the most challenging immunologic vaccination schedule was used. Contrary to studies of some other vaccines where lower antibody responses have been reported when the 6-, 10-, and 14-week schedule was employed,19,20 we observed generally higher immune responses in the Philippines using this schedule compared with the more extended 2, 4, 6 months of age schedule used in Poland. This, despite baseline antibody levels observed to be within the same range for both schedules/countries (data not shown). In addition, responses to serotypes 1, 5, and 7F in the 7vCRM group were also within the same range in both schedules/countries, suggesting no difference in natural immune priming for those serotypes. Higher responses to a pneumococcal conjugate vaccine in the Philippines were previously observed using an 11-valent mixed diphtheria and tetanus-conjugated vaccine.21,22 In these studies, immunogenicity in Filipino infants using the 6-, 10-, and 14-week schedule was greater than in Israeli or Finnish infants who were vaccinated according to a 2-, 4-, and 6-month schedule. The findings from the present study are therefore in line with these previous reports. The administration of Bacillus Calmette-Guérin (BCG) vaccine at birth as explanation for this observation can be excluded. Indeed, all subjects in Poland received BCG vaccine at birth versus ∼60% of subjects in the Philippines and a post-hoc analysis showed no differences in immune responses between subjects that received BCG vaccine at birth and those that did not (results not shown). Genetic factors, early exposure or pharyngeal carriage of pneumococcal serotypes, and early exposure to bacteria with cross-reacting antigens have been proposed as possible factors influencing the higher response to pneumococcal vaccines observed in Filipino infants.22
In Poland, anti-pneumococcal antibody GMCs in the PHiD-CV group were significantly lower for 5 of the 7 common serotypes, and significantly higher for serotypes 18C and 19F, than those observed in the 7vCRM group. Higher responses in PHiD-CV recipients than 7vCRM recipients for anti-pneumococcal antibody GMCs and OPA GMTs against serotypes 18C and 19F were consistently observed for both schedules. For the other serotypes in common, ELISA GMCs and OPA GMTs were usually lower for PHiD-CV compared with 7vCRM groups in European populations.6,7 This was not the case in the Philippines where responses for both vaccines were within the same range for most serotypes.
In both schedules, the additional serotypes 1, 5, and 7F contained in the PHiD-CV vaccine were clearly immunogenic, conferring rates of antibody concentrations ≥0.2 μg/mL and OPA seropositivity in PHiD-CV recipients that were substantially higher than those in recipients of 7vCRM not containing these serotypes. Similarly, a good response to protein D has been observed in all PHiD-CV recipients for both schedules. Immune responses against cross-reactive serotypes 6A and 19A were also observed in both schedules.
In 2003, the WHO agreed that new pneumococcal conjugate vaccines could be compared with 7vCRM based on the serological threshold of 0.35 μg/mL (WHO reference laboratory ELISA without 22F absorption), derived from results from 3 key efficacy studies with 7 or 9-valent CRM-conjugate vaccines.16 An ELISA including adsorption of serotype 22F polysaccharide to increase the assay specificity (GSK's 22F-ELISA)14,15 was used to measure the pneumococcal serotype specific total IgG antibodies in this study. It has been shown that a threshold of 0.20 μg/mL using GSK's 22F-ELISA is equivalent to the 0.35 μg/mL threshold using the WHO reference laboratory ELISA without 22F inhibition.15 In this study the use of either thresholds (both with GSK's 22F-ELISA) did not alter the study conclusions.
The immunogenicity profiles of both pneumococcal vaccines demonstrated some marked differences. However, we consider it unlikely that these differences between the 2 vaccines will translate into clinically significant differences in protection against invasive pneumococcal disease. First, the percentage of subjects who reached an anti-pneumococcal antibody concentration ≥0.2 μg/mL after primary vaccination was within the same range for most of the serotypes common to both vaccines.
Secondly, it is generally accepted that for pneumococcal conjugate vaccines, OPA directly relates to protection against infection23–25 and that the percentage of subjects with OPA titer ≥8 reflects well vaccine effectiveness.14,18,25 In this study, the percentage of subjects who reached an OPA titer ≥8 was similar for both vaccines for most common serotypes, suggesting similar protective efficacy against invasive disease due to these serotypes for both schedules.
Comparison of post-primary immunogenicity does not by itself, however, provide an understanding of the relative overall public health impact of new vaccines with different serotype compositions. Although the 7vCRM vaccine has been estimated to cover 80% to 90% of serotypes responsible for IPD in young children in North America and Australia, the coverage is lower in other parts of the world especially Africa, Latin America, and Asia.26 Higher valent vaccine formulations such as the 10-valent PHiD-CV and 13-valent CRM-conjugated vaccine in development27,28 will increase vaccine coverage of IPD-causing serotypes in these regions29 but this does not take into account that vaccine efficacy varies by serotype and is usually less than 100%.30 A recent approach to estimate the overall vaccine impact on IPD in different countries uses the results of immunogenicity comparisons, along with published serotype-specific vaccine effectiveness values for 7vCRM30 and country IPD serotype distribution. A preliminary report of the application of this IPD-Impact-Estimate using the 0.2 μg/mL ELISA threshold as basis of comparison and the immunogenicity data of the Filipino arm of the presented study, suggested that PHiD-CV would prevent approximately 79% of IPD in the Philippines while 7vCRM would prevent 62%.31 The magnitude of the effectiveness expected to be provided by PHiD-CV depends on the importance of the additional serotypes 1, 5, and 7F (only contained in the PHiD-CV vaccine) in the total invasive pneumococcal disease burden.32 Together serotypes 1, 5, and 7F are estimated to represent at least 13% of invasive pneumococcal disease isolates in young children in Europe, and at least 20% of invasive isolates in children from Africa, Asia, and Latin America.26 Serotypes 1 and 5 are particularly implicated as causes of invasive disease in older children, as causes of outbreaks of pneumococcal invasive disease including meningitis, and serotype 1 as a cause of complicated pneumonia.32
In conclusion, PHiD-CV was immunogenic when coadministered with DTPw-HBV/Hib and poliovirus vaccines. The immunogenicity of PHiD-CV coadministered with DTPw at 2, 4, and 6 months of age in Poland appeared similar to the immunogenicity of PHiD-CV coadministered with acellular pertussis DTP-based vaccines elsewhere in Europe. PHiD-CV immunogenicity observed after the challenging the 6-, 10-, and 14-week primary schedule in the Philippines exceeded that observed in Poland and was comparable with the immune responses measured after primary vaccination with 7vCRM. The PHiD-CV vaccine that contains 3 additional serotypes (1, 5, and 7F) was immunogenic for all vaccine serotypes and has potential to provide substantial benefits to children in the prevention of invasive pneumococcal disease.
The authors thank the parents and their children who participated in these trials; the investigators, clinicians, study nurses, and other staff members for contributing in many ways to the study, in particular Drs. K. Kulczyk, J. Pejcz, B. Białynicka-Birula, and E. Majda-Stanisławska from Poland, and C. Matela, M. Hernandez, F. Reyes, I. Aquino, L. Casidsid, C. Cuaresma, F. Bajaro, W. Dacasin, E. La Valle from The Philippines; the clinical and serological laboratory teams of GlaxoSmithKline Biologic for their contribution to this study, in particular Aurélie Fanic for statistical analysis and Mireille Venken for clinical report writing. Medical writing was provided by Dr. Joanne Wolter (freelance) and editorial assistance and manuscript coordination were provided by Dr. Christine Vanderlinden (GlaxoSmithKline Biologicals).
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