Pfizer's 25-Valent Pediatric Pneumococcal Vaccine Shows Phase 2 Data: Serotype 3 Antibody Levels About 15 Times Higher Than Current Vaccine, Now in Phase 3
Pfizer on October 24 presented detailed Phase 2 results for its investigational 25-valent pneumococcal conjugate vaccine candidate, PF-07872412 (25vPnC), in an oral session at IDWeek 2026 in Washington, D.C. In the study, a four-dose series of 25vPnC elicited robust immune responses against all 25 serotypes in healthy infants, with safety and tolerability comparable to PREVNAR 20 and no related serious adverse events identified.
The headline finding involved serotype 3, which accounts for 10.6 percent of invasive pneumococcal disease in U.S. children under five and has historically been a weak spot for existing vaccines. One month after dose 3, serotype 3 antibody geometric mean concentrations were 8.8-fold higher with 25vPnC than with PREVNAR 20 (4.22 versus 0.48); one month after the dose 4 booster, they were approximately 15-fold higher (13.85 versus 0.92). Pfizer said the candidate uses next-generation conjugate technology designed specifically to strengthen the serotype 3 response.
Beyond the 20 serotypes covered by PREVNAR 20, 25vPnC adds five more (15A, 23A, 23B, 24F and 35B) estimated to account for roughly 30 percent of additional pediatric invasive pneumococcal cases in the U.S.; together, the 25 serotypes are responsible for approximately 84 percent of such cases in children under five. The randomized Phase 2 trial (NCT06524414) dosed healthy infants at 2, 4, 6 and 12 to 15 months of age.
"These encouraging data build on more than 25 years of progress in protecting children from serious pneumococcal disease with PREVNAR vaccines," said Annaliesa Anderson, Ph.D., Senior Vice President and Chief Vaccines Officer at Pfizer. "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."
Pfizer said the data support its ongoing Phase 3 program: three pediatric Phase 3 studies began earlier in 2026 with up to 6,830 participants randomized to 25vPnC or PREVNAR 20, and enrollment in a three-lot consistency study is complete. For adults, the company plans to move a fifth-generation 35-valent candidate into clinical development by the end of 2026, pending regulatory alignment. The 25vPnC candidate remains investigational and is not approved by any regulator.
Source: GSM · USA (original Chinese edition)
Photo: 图：实验室人员抽取疫苗药液（资料图）。照片：John Keith 摄，公共领域，经 Wikimedia Commons。Photo: A laboratory worker draws vaccine from a vial (file photo). Photo by John Keith, public domain, via Wikimedia Commons.
