A RANDOMISED non-inferiority trial in The Gambia has shown that a two-dose primary schedule of pneumococcal conjugate vaccine (PCV13) provides equivalent clinical protection to the traditional three-dose regimen.
The trial enrolled 2,531 healthy infants in rural Gambia, randomising them to receive either two PCV13 doses at 6 and 14 weeks (2p+0 schedule) or three doses at 6, 10, and 14 weeks (3p+0 schedule), with no booster. Participants were followed until 2 years of age, with outcomes including clinical pneumonia, radiologically confirmed pneumonia, and invasive pneumococcal disease. Immunogenicity was also assessed.
Radiologically confirmed pneumonia occurred in 5.4% of children in the two-dose group and 5.5% in the three-dose group (risk difference: -0.1%, 95% CI: -1.5–1.3), satisfying the non-inferiority margin. Clinical pneumonia occurred in 15.2% (two-dose) versus 14.9% (three-dose); confirmed invasive pneumococcal disease cases were low in both groups. Geometric mean concentrations of anti-capsular IgG were slightly lower in the two-dose group but exceeded protective thresholds for most serotypes.
The results indicate that a two-dose primary schedule without booster can provide sufficient protection in high-transmission, resource-limited settings. This could enable reduced-cost vaccination programmes while maintaining efficacy.
Reference
Mackenzie G et al. Impact of a two-dose compared to three-dose schedule of infant pneumococcal conjugate vaccination on radiological pneumonia in rural Gambia. Abstract 2396. ESPID Annual Meeting, 26-30 May, 2025.
