Efficacy of different pneumococcal conjugate vaccine schedules against pneumonia,hospitalisation, and mortality: Re-analysis of a randomised trial in The Gambia

Background

Pneumococcal conjugate vaccines (PCV) reduce disease due to Streptococcus pneumoniae. We aimed to determine the efficacy of different PCV schedules in Gambian children.

Methods

We reanalysed data from a randomised placebo-controlled trial. Infants aged 6–51 weeks were allocated to three doses of nine-valent PCV (n = 8718) or placebo (n = 8719) and followed until age 30 months. We categorised participants to compare: (a) a first dose at age 6 or 10 weeks, (b) intervals of 1 or 2 months between doses, and (c) different intervals between second and third doses. The primary endpoint was first episode of radiologic pneumonia; other endpoints were hospitalisation and mortality. Using the placebo group as the reference population, Poisson regression models were used with follow-up after the first dose to estimate the efficacy of each schedule and from age 6 weeks to estimate the incidence rate difference between schedules.

Results

Predicted efficacy in the groups aged 6 weeks (n = 2467, 154 events) or 10 weeks (n = 2420, 106 events) at first dose against radiologic pneumonia were 32% (95% CI 19–43%) and 33% (95% CI 21–44%), against hospitalisation 14% (95% CI 3–23%) and 17% (95% CI 7–26%), and against mortality 17% (95% CI −3 to 33%) and 16% (95% CI −3 to 32%) respectively. Predicted efficacy in the groups with intervals of 1 month (n = 2701, 133 events) or 2 months (n = 1351, 58 events) between doses against radiologic pneumonia were 33% (95% CI 20–44%) and 36% (95% CI 24–46%), against hospitalisation 15% (95% CI 5–24%) and 18% (95% CI 8–27%), and against mortality 17% (95% CI −2 to 33%) and 13% (95% CI −8 to 29%) respectively. Efficacy did not differ by interval between second and third doses, nor did the incidence rate difference between schedules.

Conclusions

We found no evidence that efficacy or effectiveness of PCV9 differed when doses were given with modest variability around the scheduled ages or intervals between doses.