Pfizer Inc. (NYSE: PFE) today announced detailed results across serotypes from a Phase 2 study (NCT06524414) for its investigational 25-valent pneumococcal conjugate vaccine candidate, PF-07872412 (25vPnC), in infants. In the study, a four-dose series of 25vPnC elicited robust immune responses against all 25 serotypes and showed safety and tolerability comparable to four doses of PREVNAR 20® (Pneumococcal 20-valent Conjugate Vaccine). These findings were shared today in an oral presentation at IDWeek 2026 in Washington, D.C.1
These data support the ongoing Phase 3 development program for 25vPnC, which, if successful, could help provide protection against serotypes collectively responsible for approximately 84% of invasive pneumococcal disease (IPD) cases among children under five years of age in the U.S.2
"These encouraging data build on more than 25 years of progress in protecting children from serious pneumococcal disease with PREVNAR vaccines. By expanding serotype coverage and applying next-generation technology to the historically challenging serotype 3, this candidate aims to extend the substantial reductions in disease that existing vaccines have achieved. If successful, it could help provide children with the broadest protection against invasive pneumococcal disease to date."
- Annaliesa Anderson, Ph.D., Senior Vice President and Chief Vaccines Officer, Pfizer
Phase 2 Study Results Across 25 Serotypes
The Phase 2 study is evaluating the safety, tolerability, and immunogenicity of the 25-valent vaccine candidate (25vPnC) compared with PREVNAR 20 in healthy infants. These data build on results announced earlier this year showing:
- Robust immune responses against all 25 serotypes one month after Dose 3 and one month after Dose 4, including against all five new serotypes (15A, 23A, 23B, 24F, and 35B). Rates of local reactions, systemic events, and adverse events were balanced across the 25-valent vaccine candidate and PREVNAR 20 groups in the Phase 2 trial. Adverse events were consistent with conditions commonly diagnosed in this age group. There were no related serious adverse events identified in the study. 1
- The 25-valent vaccine candidate elicited an enhanced immune response against serotype 3 compared with PREVNAR 20, generating GMCs that were 8.8-fold higher one month after Dose 3 and approximately 15-fold higher one month after Dose 4. 1 It utilizes next-generation technology specifically designed to elicit a more robust immune response against serotype 3, which accounts for 10.6% of all IPD in children under five years old in the U.S. 2
- 25-valent vaccine candidate also elicited functional responses in the opsonophagocytic activity assay (OPA) one month after Dose 4 for all 25 target serotypes, demonstrating booster effects. 1 This result demonstrates the vaccine candidate's potential to generate antibodies that can contribute to the functional killing of pneumococcal bacteria. 3
Detailed results from the presentation can be found online here.
Continuing Pfizer's Commitment to Pneumococcal Disease Prevention
These results build on Pfizer's long-standing commitment to protecting people from pneumococcal disease. Pfizer is advancing two next-generation pneumococcal conjugate vaccine candidates across pediatric and adult populations.
- In children, 25vPnC is being evaluated in three Phase 3 studies that began earlier in 2026, with up to 6,830 participants randomized to receive 25vPnC or PREVNAR 20. 4,5,6 Additionally, Pfizer has completed enrollment of a Phase 3 study to demonstrate the consistency of three manufacturing lots of 25vPnC. 7
- The five new serotypes (15A, 23A, 23B, 24F, and 35B) are estimated to account for an additional ~30% of pediatric invasive pneumococcal disease cases in the U.S. compared with PREVNAR 20. 2 It also uses next-generation technology designed to improve responses to serotype 3, which accounts for 10.6% of invasive pneumococcal disease in U.S. children under five years of age. 1,2
- In adults, Pfizer plans to bring a fifth-generation, 35-valent vaccine candidate into clinical development by the end of 2026, pending alignment from regulatory authorities.
