25-valent pneumococcal vaccine hits all serotypes in infant trial

An investigational 25-valent pneumococcal conjugate vaccine (25vPnC; PF-07872412) given as a 4-dose infant series generated immune responses against all 25 included serotypes, with safety and tolerability comparable to 4 doses of PCV20 (Prevnar 20), according to phase 2 data presented October 24, 2026, at IDWeek 2026 in Washington, DC.¹ The candidate adds 5 serotypes — 15A, 23A, 23B, 24F, and 35B — to the 20 covered by the currently licensed vaccine.¹

"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," said Annaliesa Anderson, PhD, senior vice president and chief vaccines officer at Pfizer, in a statement.¹ The manufacturer estimates that the 25 serotypes account for roughly 84% of invasive pneumococcal disease (IPD) cases in US children younger than 5 years.²

25vPnC phase 2 trial design and immunogenicity in healthy infants

The ongoing phase 2 study (NCT06524414) is a randomized trial evaluating the safety, tolerability, and immunogenicity of 25vPnC against licensed pneumococcal conjugate vaccines, including PCV20, in healthy infants.³ Enrollment began in July 2024, and infants received a 4-dose series at approximately 2, 4, 6, and 12 to 15 months of age, matching the schedule used for routine pneumococcal conjugate vaccination in the United States.¹

One month after dose 3 and again one month after dose 4, the candidate elicited immune responses against all 25 serotypes, including each of the 5 serotypes not covered by PCV20.¹ Functional responses measured by opsonophagocytic activity assay were seen for all 25 target serotypes one month after dose 4, with evidence of a booster effect.¹ Opsonophagocytic activity is the standard functional correlate used in pneumococcal vaccine development because it reflects antibody-mediated killing of the organism rather than binding alone.¹

Serotype 3 response and safety profile of 25vPnC versus PCV20

The most clinically notable signal involved serotype 3, which remains a persistent cause of pneumococcal disease despite its inclusion in PCV13 and PCV20. Geometric mean concentrations against serotype 3 were 8.8-fold higher with 25vPnC than with PCV20 one month after dose 3 and approximately 15-fold higher one month after dose 4.¹ Pfizer attributes the difference to a modified conjugation approach intended to improve immunogenicity against that serotype specifically.¹ Serotype 3 accounts for 10.6% of IPD in US children younger than 5 years.²

Rates of local reactions, systemic events, and adverse events were balanced between the 25vPnC and PCV20 groups, and reported events were consistent with conditions commonly diagnosed in this age group.¹ No related serious adverse events were identified.¹ Reactogenicity after PCV20 in infants on a 4-dose schedule commonly includes irritability, injection-site pain, drowsiness, decreased appetite, and fever, each reported in more than 10% of recipients.¹

Pediatric IPD burden and current pneumococcal vaccine recommendations

Routine infant pneumococcal conjugate vaccination has sharply reduced IPD in young children since PCV7 was introduced in 2000, but residual disease is increasingly driven by serotypes outside existing vaccine formulations, a pattern of replacement that has followed each generation of conjugate vaccine. Current practice reflects that: the CDC recommends a dose of PCV15 or PCV20 at 2, 4, 6, and 12 through 15 months of age for all children, with catch-up and risk-based schedules for older children and those with immunocompromising or chronic conditions.⁴

Pfizer estimates the 5 added serotypes account for approximately 30% more pediatric IPD cases in the United States than PCV20 covers.² Whether broader serotype coverage translates into measurable reductions in disease incidence, however, is a question immunogenicity data cannot answer, and the 5 new serotypes carry no established correlate of protection in infants.

25vPnC phase 3 program

Three phase 3 studies began earlier in 2026, randomizing up to 6830 participants to 25vPnC or PCV20, with a separate study assessing consistency across 3 manufacturing lots.¹ Those trials, spanning infants and a catch-up population of older children and adolescents, will determine whether the candidate meets the immunologic thresholds regulators require for licensure. For pediatricians, nothing changes in the near term: PCV15 and PCV20 remain the recommended options, and any shift in the infant schedule would follow FDA review and subsequent ACIP deliberation.

References

1. Pfizer's 25-valent pediatric pneumococcal conjugate vaccine candidate shows robust phase 2 data at IDWeek 2026. News release. Pfizer Inc. October 24, 2026. Accessed October 26, 2026. https://www.businesswire.com/news/home/20261024078788/en/

2. Centers for Disease Control and Prevention. Active Bacterial Core Surveillance (ABCs) surveillance reports, 2020-2024. Accessed October 26, 2026. https://www.cdc.gov/abcs/reports/index.html

3. A study to learn about how a new pneumococcal vaccine works in infants. ClinicalTrials.gov identifier: NCT06524414. Accessed October 26, 2026. https://clinicaltrials.gov/study/NCT06524414

4. Centers for Disease Control and Prevention. Pneumococcal vaccine recommendations. Accessed October 26, 2026. https://www.cdc.gov/pneumococcal/hcp/vaccine-recommendations/index.html