Global pharma powerhouse Pfizer’s experimental 25-valent pneumococcal vaccine has delivered promising Phase 2 results in infants.

 

This by generating immune responses against all 25 targeted bacterial serotypes and demonstrating safety and tolerability comparable to the company’s existing PREVNAR 20 vaccine, according to data presented at IDWeek 2026 in Washington, D.C.

 

The findings could mark a significant step towards broader protection against invasive pneumococcal disease (IPD), a serious infection that can cause life-threatening complications in young children.

 

The investigational vaccine, PF-07872412, also known as 25vPnC, is designed to expand protection beyond the 20 serotypes covered by PREVNAR 20. If successful in further clinical trials, it could target serotypes collectively responsible for approximately 84% of invasive pneumococcal disease cases among children under five in the United States.

 

“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," said Annaliesa Anderson, Senior Vice President and Chief Vaccines Officer, Pfizer.

 

The Phase 2 study evaluated the vaccine’s safety, tolerability and immunogenicity in healthy infants, comparing it with PREVNAR 20.

 

Results showed that a four-dose series of the experimental vaccine generated robust immune responses against all 25 targeted serotypes, both after the third dose and after the fourth dose.

 

The five additional serotypes — 15A, 23A, 23B, 24F and 35B — are estimated to account for approximately 30% of pediatric invasive pneumococcal disease cases in the US beyond those associated with the serotypes covered by PREVNAR 20.

 

The vaccine also demonstrated a markedly stronger immune response against serotype 3, a particularly challenging target that accounts for 10.6% of invasive pneumococcal disease cases among US children under five.

 

Pfizer reported that antibody geometric mean concentrations against serotype 3 were 8.8 times higher with the investigational vaccine than with PREVNAR 20 one month after the third dose. One month after the fourth dose, the levels were approximately 15 times higher.

 

The candidate uses next-generation technology specifically designed to improve the immune response against serotype 3, potentially addressing an important gap in pneumococcal disease prevention.

 

The Phase 2 findings also indicated that the candidate had a safety and tolerability profile comparable to PREVNAR 20.

 

Rates of local reactions, systemic events and adverse events were balanced between the two study groups. Reported adverse events were consistent with conditions commonly diagnosed in infants, and investigators identified no related serious adverse events.

 

The vaccine also triggered functional immune responses against all 25 targeted serotypes in an opsonophagocytic activity (OPA) assay after the fourth dose. This laboratory test assesses the ability of antibodies to help immune cells recognise and kill bacteria.

 

The results suggest that the candidate could generate antibodies capable of contributing to the functional killing of pneumococcal bacteria, although further clinical development will be needed to establish its effectiveness in preventing disease.

 

Pfizer is advancing the vaccine through a Phase 3 development programme, with three studies launched earlier in 2026 involving up to 6,830 participants. The trials are comparing 25vPnC with PREVNAR 20 in pediatric populations.

 

The company has also completed enrolment in a separate Phase 3 study designed to assess the consistency of three manufacturing lots of the candidate vaccine.