Pfizer reported positive Phase 2 results for its investigational 25-valent pneumococcal conjugate vaccine (25vPnC) in infants, showing significantly stronger immune responses against serotype 3 compared with PREVNAR 20. The findings support a pivotal pediatric Phase 3 program and advance Pfizer’s next-generation pneumococcal vaccine strategy.
By: Regulatory Desk
Pfizer presented positive preliminary Phase 2 data for its investigational 25-valent pneumococcal conjugate vaccine candidate, PF-07872412 (25vPnC), in healthy infants, highlighting markedly improved immune responses against serotype 3 versus PREVNAR 20. The randomized study began enrollment in July 2024, and the results were presented at the 14th International Society of Pneumonia & Pneumococcal Diseases (ISPPD) meeting in Copenhagen in 2026. The data support Pfizer’s ongoing pediatric Phase 3 program evaluating the next-generation vaccine candidate in infants.
The Phase 2 trial (NCT06524414) evaluated a four-dose infant vaccination schedule administered at 2, 4, 6, and 12–15 months of age. Investigators compared the safety, tolerability, and immunogenicity of 25vPnC with PREVNAR 20. One month after Dose 3, geometric mean titers against serotype 3 were 8.8-fold higher with 25vPnC than with PREVNAR 20. One month after Dose 4, titers were approximately 15-fold higher with the investigational vaccine candidate.
Despite broad reductions in pneumococcal disease following the introduction of higher-valent pneumococcal conjugate vaccines, serotype 3 remains a significant cause of invasive pneumococcal disease and complicated pneumonia in children. Pfizer estimates that 25vPnC could provide coverage against approximately 90% of disease-causing pneumococcal serotypes in children younger than five years of age. The expanded coverage includes five additional serotypes 15A, 23A, 23B, 24F, and 35B along with enhanced immune protection against serotype 3.
Pfizer’s fourth-generation pneumococcal vaccine candidate builds on the 20 serotypes already included in PREVNAR 20. Beyond expanding serotype coverage, the vaccine incorporates Pfizer’s proprietary conjugation and carrier protein technology intended to enhance immunogenicity against serotype 3, one of the most persistent drivers of residual pneumococcal disease.
The Phase 2 study assessed local and systemic reactogenicity within seven days after vaccination, alongside adverse events and serious adverse events. No new safety signals were observed, with reactogenicity profiles comparable to licensed pneumococcal conjugate vaccines. Injection-site redness, swelling, and pain were the most commonly reported local reactions.
Annaliesa Anderson, Senior Vice President and Chief Vaccines Officer at Pfizer, said the findings reinforce confidence in expanding serotype coverage while improving protection against persistent disease drivers such as serotype 3. Following discussions with regulatory authorities, Pfizer initiated a pivotal pediatric Phase 3 program in May 2026.
The Phase 3 pediatric studies will enroll up to 2,400 healthy infants receiving either 25vPnC or PCV20 (PREVNAR 20) across the same four-dose schedule administered at 2, 4, 6, and 12–15 months of age. The studies will evaluate safety, tolerability, and immunogenicity across all vaccination time points.
Separately, Pfizer disclosed plans to advance a distinct fifth-generation 35-valent adult pneumococcal vaccine candidate intended for the adult market. The adult program aims to further expand serotype coverage while improving immune responses against clinically important strains, including serotype 3. Clinical development of the 35-valent adult candidate is expected to begin by the end of 2026, pending regulatory alignment.
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