Already after 2 PHiD-CV doses, 87.8% to 99.4% of subjects had ELISA antibody concentrations ≥0.2 μg/mL for serotypes 1, 4, 5, 7F, 9V, 14, 18C, and 19F, at least 64.1% of subjects reached the ELISA threshold for serotype 6B and at least 75.0% for serotype 23F. Results within the same range were obtained in the 7vCRM group for the serotypes common to both PHiD-CV and 7vCRM except that the percentage of subjects with antibody concentrations ≥0.2 μg/mL was lower for serotype 6B and higher for serotype 18C compared with PHiD-CV. Two doses of PHiD-CV induced OPA titers ≥8 for serotypes 4, 7F, 9V, 14, and 23F in at least 96.8% of subjects. The lowest OPA response was observed for serotypes 1 (48.8% of subjects with titers ≥8) and 18C (59.8%). The percentage of subjects with OPA titer ≥8 was lower in the 7vCRM group for serotypes 6B and 19F compared with the PHiD-CV pooled groups and higher for serotype 18C.
The third PHiD-CV dose had an important impact on the percentage of subjects with ELISA antibody concentrations ≥0.2 μg/mL for 6B (increased from 64.1% to 89.9%) and 23F (increased from 75.0% to 93.7%). The same observation was made for the third 7vCRM dose for which the impact on 6B was even more marked (increased from 30.8% to 92.1%). For most serotypes, antibody GMCs were higher after the third dose than after the second dose, with the most marked increase observed for both vaccines for serotypes 6B and 23F. After the third vaccine dose, the percentage of subjects with OPA titers ≥8 increased for serotypes 6B, 18C, and 19F in both groups, for serotype 5 in the PHiD-CV group, and for serotype 23F in the 7vCRM group. In both groups, the third dose increased OPA GMTs for all common serotypes and for serotypes 5 and 7F in the PHiD-CV group.
A marked decline in ELISA antibody GMCs was observed in the time period after the third primary dose and before booster vaccination. Nevertheless, before the booster dose over 80.0% to 94.8% of PHiD-CV primed subjects still had persisting anti-pneumococcal antibody concentrations ≥0.2 μg/mL for all vaccine serotypes except serotype 1 (53.9%). In the 7vCRM group, 77.2% to 96.0% of vaccinees still had anti-pneumococcal antibody concentrations ≥0.2 g/mL for each of the shared serotypes but lower persistence rates were observed for serotypes 6B (57.8%) and 19F (46.6%). In PHiD-CV primed subjects, the persistence of antibody concentrations ≥0.2 μg/mL for serotypes 1, 5, and 7F ranged between 53.9% and 94.8%, compared with less than 4.8% in 7vCRM-primed subjects. It is noteworthy that for serotypes 4, 9V, and 23F, despite the lower post-primary antibody GMCs observed in PHiD-CV-primed subjects compared with 7vCRM-primed subjects, GMCs were in the same range before the booster vaccination, indicating a less pronounced decline of antibody concentrations in PHiD-CV-primed subjects for those serotypes. OPA GMTs also declined over the same period, however, a high proportion of subjects still had OPA titers ≥8 before booster for serotypes 7F (95.8%), 9V (96.4%), 14 (93.8%), 19F (76.8%), and 23F (88.7%) in the PHiD-CV groups and serotypes 9V (96.9%), 14 (99.2%), and 23F (90.3%) in 7vCRM primed subjects. Low persistence was observed for serotype 18C in both PHiD-CV (37.9%) and 7vCRM (28.3%) primed subjects and for 19F (20.6%) in 7vCRM primed subjects. After booster vaccination both ELISA GMCs and OPA GMTs were restored to above post-primary level for all vaccine serotypes in both vaccine groups.
Immunogenicity to PD
After primary vaccination, all except 1 PHiD-CV vaccinee had measurable antibodies against PD (≥100 EL.U/mL) with anti-PD antibody GMCs of 1715.5 to 2114.0 EL.U/mL compared with 72.3 EL.U/mL in the 7vCRM group (Table 6). At least 94.0% of PHiD-CV vaccinees still had measurable antibodies before booster vaccination and a booster response within the same range was observed in the 3 PHiD-CV groups.
In recent years, the availability of new vaccines has led to an increase in the number of injections required to complete recommended pediatric vaccine schedules. The use of DTP-based combination vaccines, which include hepatitis B, polio, and Hib antigens, such as employed in this study, facilitate the inclusion of new vaccines into pediatric immunization programs. N. meningitidis serogroup C (MenC) conjugate vaccines are now also increasingly being incorporated into infant schedules. In this study, we have sought to establish whether the candidate S. pneumoniae conjugate PHiD-CV vaccine is compatible with these other frequently used pediatric vaccines, in particular different MenC-conjugated vaccines.
Considering the 3 PHiD-CV groups with different MenC conjugate vaccines, ELISA IgG and functional OPA immune responses were elicited against all vaccines serotypes after primary vaccination, followed by strong booster responses indicating the induction of immunologic memory. In all 3 PHiD-CV groups, a high percentage of subjects achieved an antibody concentration of ≥0.2 μg/mL, with antibody GMCs that were within the same range for most serotypes. Post-primary OPA GMTs were within the same range for most serotypes in all 3 PHiD-CV groups. The higher response in the PHiD-CV+MenC-TT group for serotype 18C, which is conjugated to tetanus toxoid, may be related to the coadministered MenC-TT vaccine. The reason why this was not observed in the PHiD-CV+Hib-MenC-TT group despite the use of TT as carrier protein for both components of the Hib-MenC vaccine is not fully understood, but could be related to the total amount of TT-carrier protein that is different between the PHiD-CV+MenC-TT [10 μg of meningococcal serogroup C capsular polysaccharide (PSC)] conjugated to 10–20 μg of TT and 10 μg of PRP conjugated to 20–40 μg of TT) and PHiD-CV+Hib-MenC-TT (5 μg of PRP conjugated to 10–20 μg of TT and 5 μg of PSC conjugated to 3.5–12.5 μg of TT) groups. As reported elsewhere,29 the antitetanus response was the highest in the MenC-TT group and there is evidence that carrier priming can enhance immune responses to polysaccharides in subsequent doses of conjugate.30–32 Overall, the different coadministered vaccines did not result in differences in PHiD-CV pneumococccal responses that would be considered as clinically relevant. As reported by Knuf et al,29 immunogenicity was demonstrated in the 3 groups for all the coadministered vaccines including the meningococcal C conjugates. These findings indicate that the PHiD-CV candidate vaccine is compatible with other pediatric vaccines including MenC and Hib-MenC vaccines.
Although not designed for statistical comparison, the study also included a 7vCRM+Hib-MenC group. It was observed that after primary vaccination the percentages of subjects with antibody concentrations ≥0.2 μg/mL against the serotypes common to both PHiD-CV and 7vCRM vaccines were within the same range. Although post-primary GMCs were higher for some serotypes in the 7vCRM group, the decline in serotype specific antibody levels observed in the 8–12 months after primary vaccination resulted in antibody GMCs within the same range for PHiD-CV and 7vCRM primed groups before booster vaccination for serotypes 4, 9V, and 23F. Furthermore, the robust increases in ELISA and OPA responses after the PHiD-CV booster, which were in most cases of the same order of magnitude as those obtained after the 7vCRM booster, would indicate adequate priming of the immune system against all PHiD-CV vaccine serotypes.
Despite lower post-primary immunologic responses observed for some serotypes in the PHiD-CV+Hib-MenC group compared to the other PHiD-CV groups, robust booster responses were observed in all PHiD-CV groups; indicating adequate priming of the immune system.
Comparison of post-primary immunogenicity does not by itself, however, provide an understanding of the relative overall public health impact of new vaccines with a different serotype composition to the existing licensed 7-valent vaccine. 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.33 Higher valent vaccine formulations such as the 10-valent PHiD-CV and 13-valent CRM-conjugated vaccine in development34,35 will increase vaccine coverage of IPD-causing serotypes in these regions.36 Although serotype coverage can give a rough estimate of the public health impact of a new multivalent pneumococcal conjugate vaccine, this does not take into account that vaccine efficacy varies by serotype and is usually less than 100%.37 A recent approach to providing an estimate of the overall vaccine impact on IPD in different countries uses the results of immunogenicity comparisons, along with published serotype-specific vaccine effectiveness values for 7vCRM37 and country IPD serotype distribution. A preliminary report of the application of this IPD-Impact-Estimate to immunogenicity data from the present study suggested that the overall impact of PHiD-CV on IPD to be at least as high as that of 7vCRM and potentially higher in countries where the additional 3 serotypes 1, 5, and 7F cause significant disease.38
This report also followed the kinetics of the immune response from the second primary vaccination dose up to one month after booster vaccination. Overall, the kinetics for the common serotypes appear to be in the same range for the PHiD-CV and 7vCRM vaccines. It is noteworthy that, apart for serotypes 6B and 23F, at least 87.8% of subjects reached an antibody concentration of at least 0.2 μg/mL after just 2 primary doses of PHiD-CV or 7vCRM vaccine although antibody GMCs were below those achieved after 3 primary doses. For serotype 23F, 97.1% of PHiD-CV vaccinees achieved OPA titers ≥8 and for serotype 6B lower percentages of subjects reaching the ELISA and OPA thresholds were observed in 7vCRM vaccines compared with PHiD-CV vaccinees. A third dose was also required to achieve high percentages of subjects with OPA activity for serotypes 6B, 18C, and 19F (for both PHiD-CV and 7vCRM vaccinees) and for serotype 23F in 7vCRM vaccinees. Recently the use of a 2 primary dose plus booster schedule has been approved for 7vCRM in Europe with the acknowledgment that smaller proportions of infants achieve threshold ELISA antibody levels against serotypes 6B and 23F and that GMCs are lower for antibodies against most serotypes compared with those after a 3-dose infant series.39 However good booster responses were taken as an indication that 2 doses of 7vCRM would elicit adequate priming.39
In summary, assessment of immunogenicity in this study indicated that the PHiD-CV vaccine is compatible with other pediatric vaccines including MenC and Hib-MenC vaccines. PHiD-CV was immunogenic already 2 months after the second dose (with similar responses compared with the post-dose 2 responses in the 7vCRM group), as well as 1 month after the 3-dose primary course and 1 month after the booster dose.
The authors thank the parents and their children who participated in these trials. The authors would also like to acknowledge the assistance of the investigators, clinicians, study nurses and other staff members in conducting these studies, in particular all the investigators involved in these studies: U. Behre, F. Bertholdt, P. Bosch, E. Erdmann, S. Hetzinger, U. Hörnlein, M. Kimmig, K. Kindler, K. Kirsten, R. Knecht, H. P. Loch, KE. Mai, R. Mangelsdorf-Taxis, L. Maurer, S. Noll, H. Pabel, F. Panzer, C. Pauli, U. Pfletschinger, K. Pscherer, H.H. Rohé, L. Sander, H.C. Sengespeik, M. Steiner, U. Sträubler, K.J. Taube, K. Vogel, M. Völker, M. Vomstein, V. von Arnim, M.H. Wagner, A. Galaj, B. Pajek, J. Brzostek, W. Olechowski, E. Miszczak-Kowalska, J. Arístegui, A. de Vicente, J.M. Merino, X. Pérez-Porcuna, E. Muñoz, M. Moro, D. Moreno, M. Méndez, J. de la Flor, J. Marés, F. Barrio, M.J. de Torres, F. Centeno, F. Omeñaca, C. Lotz, C. Witterman, U. Jacob, U. Wachter, B. Acosta, C. López.
In addition, they would like to thank the clinical and serological laboratory teams of GSK Biologicals for their contribution to these studies as well as Karine Muller and Patricia Lommel for statistical analysis, Thomas Moens and Liliana Manciu for clinical report, Stefanie Deckers for study coordination (all from GSK Biologicals), Dr. Miriam Hynes (Freelance, United Kingdom) for medical writing, and Dr. Christine Vanderlinden (GSK Biologicals) for editorial assistance and manuscript coordination.
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Keywords:© 2009 Lippincott Williams & Wilkins, Inc.
pneumococcal conjugate vaccine; ELISA; opsonophagocytic activity