Immunogenicity following one, two, or three doses of the 7-valent pneumococcal conjugate vaccine

The aim was to identify an appropriate infant pneumococcal vaccination strategy for resource poor countries. Fijian infants received zero, one, two, or three doses of 7-valent pneumococcal conjugate vaccine (PCV) in early infancy. Following three PCV doses, geometric mean concentration (GMC) to all seven serotypes were ≥1.0 μg/mL, and >85% of children achieved antibody levels ≥0.35 μg/mL at 18 weeks. Following two doses, GMC were lower for 6B, 14, and 23F, but higher for 19F compared with three doses. Following a single dose, significant responses were seen for all serotypes post-primary series compared with the unvaccinated. By 12 months, differences between two and three doses persisted for serotype 14 only. Although GMC following three doses are higher than after two doses, the differences were small. A single dose may offer some protection for most serotypes.