The Phase 2 trial evaluated a four-dose series of the 25-valent conjugate vaccine (25vPnC) at months 2, 4, 6 and 12–15 in healthy infants, compared head-to-head with four doses of Prevnar 20. One month after the third dose, geometric mean titers for serotype 3 were 4.22 with 25vPnC versus 0.48 with Prevnar 20 (8.8-fold increase), rising to 13.85 versus 0.92 (15-fold increase) one month after dose 4. The candidate covers up to 90% of disease-causing serotypes in children under 5, including enhanced responses to serotype 3.

Based on robust Phase 2 immunogenicity and safety data, Pfizer launched a pivotal pediatric Phase 3 trial in May 2026. The randomized study will enroll approximately 2,400 infants to compare four doses of 25vPnC against the licensed 20-valent standard-of-care vaccine, assessing safety, tolerability and immunogenicity through 12–15 months of age.

To maintain leadership in the adult pneumococcal market, Pfizer is advancing a fifth-generation conjugate vaccine covering 35 serotypes, including critical residual drivers like serotype 3. Subject to regulatory alignment, this adult candidate is slated to enter clinical development by the end of 2026 to broaden serotype coverage and enhance immune responses.