Children received PCV7 at 2 and 4 months (2-dose group), or at 2, 4 and 11 months (2 + 1-dose group), or no PCV7 (controls) before 1 year of age. All children received a PCV7 dose at 24 months of age.
At the age of 12 months, the 2 + 1-dose group had higher IgG levels and functional antibody levels, compared to the 2-dose group for all serotypes, but at 25 months the difference between the 2-dose and 2 + 1-dose groups had disappeared for most serotypes. The kinetics of opsonophagocytic antibodies were in line with the specific IgG antibody levels for most serotypes, although differences between the 2-dose and the 2 + 1-dose group were more pronounced in OPA activity as compared to the IgG levels especially at the age of 24 months.
Delaying the booster dose from 11 months to 24 months after 2 primary doses resulted in significantly higher OPA GMTs one month after the booster dose. This must, however, be balanced against the risk of leaving children unboosted between the age of 11 and 24 months at a time when disease risk is still high. Local decisions about the timing of a booster dose should also take into account vaccine coverage and the indirect herd effect in a well vaccinated population.
Trial registration clinicaltrials.gov Identifier: .