Immunogenicity of seven-valent pneumococcal conjugate vaccine administered at 6, 14 and 40 weeks of age in South African infants.

BACKGROUND

The high cost of pneumococcal conjugate vaccine (PCV) and local epidemiological factors contributed to evaluating different PCV dosing-schedules. This study evaluated the immunogenicity of seven-valent PCV (PCV7) administered at 6-weeks; 14-weeks and 9-months of age.

METHODS

250 healthy, HIV-unexposed infants were immunized with PCV7 concurrently with other childhood vaccines. Serotype-specific anti-capsular IgG concentrations were measured one-month following the 1(st) and 2(nd) PCV-doses, prior to and two-weeks following the 3(rd) dose. Opsonophagocytic killing assay (OPA) was measured for three serotypes following the 2(nd) and 3(rd) PCV7-doses. Immunogenicity of the current schedule was compared to a historical cohort of infants who received PCV7 at 6, 10 and 14 weeks of age.

RESULTS

The proportion of infants with serotype-specific antibody ≥ 0.35 µg/ml following the 2(nd) PCV7-dose ranged from 84% for 6B to ≥ 89% for other serotypes. Robust antibody responses were observed following the 3(rd) dose. The proportion of children with OPA ≥ 8 for serotypes 9V, 19F and 23F increased significantly following the 3(rd) PCV7-dose to 93.6%; 86.0% and 89.7% respectively. The quantitative antibody concentrations following the 2(nd) PCV7-dose were comparable to that after the 3(rd) -dose in the 6-10-14 week schedule. Geometric mean concentrations (GMCs) following the 3(rd) PCV7-dose were higher for all serotypes in this study compared to the historical cohort.

CONCLUSIONS

The studied PCV7 dosing schedule induced good immune responses, including higher GMCs following the 3(rd-)dose at 9-months compared to when given at 14-weeks of age. This may confer longer persistence of antibodies and duration of protection against pneumococcal disease.