Pfizer Advances Next-Gen Paediatric Vaccine to Phase 3

Pfizer has announced the advancement of its pivotal paediatric pneumococcal vaccine programme following encouraging data from its Phase 2 clinical trial. 

The company has initiated its Phase 3 clinical trial for an investigational 25-valent pneumococcal conjugate vaccine candidate, designated PF-07872412 or 25vPnC, in infants. 

Alongside this milestone, Pfizer has unveiled plans to progress its adult vaccine strategy by moving straight to a fifth-generation 35-valent candidate.

Strong immunogenicity shown in phase 2 results

The decision to progress into a Phase 3 programme follows positive data from a Phase 2 study evaluating the safety, tolerability and immunogenicity of a four-dose series of the 25vPnC candidate in healthy infants. In this randomised trial, which began initial enrolment in July 2024, participants received either the 25vPnC candidate or the existing licensed standard-of-care vaccine, PREVNAR 20, at two, four, six and 12-15 months of age.

Preliminary findings from the study were delivered during an oral presentation at the 14th meeting of the International Society of Pneumonia & Pneumococcal Diseases (ISPPD) in Copenhagen, Denmark. The results showed robust immune responses across all 25 included serotypes. Crucially, the investigational vaccine elicited an enhanced response against serotype 3, which continues to be a major cause of invasive pneumococcal disease and complicated pneumonia in young children.

Data revealed that one month after the third dose, geometric mean titers for serotype 3 were 8.8-fold higher in infants given 25vPnC than in those who received PREVNAR 20, with scores of 4.22 versus 0.48 respectively. One month after the fourth dose, the gap widened further, with 25vPnC producing a serotype 3 immunogenicity response approximately 15-fold higher than PREVNAR 20, recording titers of 13.85 compared to 0.92.

Broader disease coverage and safety

The 25vPnC candidate builds upon the 20 serotypes already included in PREVNAR 20 by introducing five new serotypes: 15A, 23A, 23B, 24F and 35B. This addition expands protection to cover up to 90% of disease-causing serotypes in children under five years of age, representing an additional 25% coverage of invasive pneumococcal disease cases compared to PCV20.

In terms of safety, the investigational vaccine was well-tolerated with no safety concerns identified during the Phase 2 study. The safety and tolerability profile remained consistent with currently approved pneumococcal vaccines, with the most common local reactions being typical injection site symptoms such as redness, swelling or pain.

“For more than 25 years, our vaccines have helped protect children from pneumococcal disease, yet a significant disease burden remains,” said Annaliesa Anderson, Ph.D., Senior Vice President and Chief Vaccines Officer, Pfizer. 

“These Phase 2 results reinforce our confidence in a next-generation vaccine designed to expand protection across serotypes while improving responses to key residual disease drivers such as serotype 3. We are advancing our Phase 3 programme with the goal of delivering broader and more durable protection for children.”

Launching the paediatric phase 3 programme

Based on the robust immune responses observed across the Phase 2 programme and following collaborative discussions with regulatory authorities, Pfizer officially initiated its pivotal paediatric Phase 3 programme in May 2026. The company remains confident that the candidate will meet the necessary non-inferiority thresholds required in this definitive stage of testing.

The upcoming Phase 3 studies will assess the safety, tolerability and immunogenicity of 25vPnC in up to 2,400 healthy children. Participants will be allocated to receive the exact same vaccine for all four scheduled doses, comparing 25vPnC directly to the licensed 20-valent standard-of-care vaccine at two, four, six and 12 to 15 months of age.

Evolution of the adult vaccine strategy

Simultaneously, Pfizer has chosen a direct pathway to maintain its long-term market leadership within the adult sector. The biopharmaceutical firm has decided to bypass intermediate clinical steps and move straight to a fifth-generation adult vaccine candidate that covers 35 serotypes.

This adult candidate will leverage Pfizer's proprietary next-generation technology to enhance immunogenicity for critical strains, including serotype 3, while expanding overall serotype coverage. Pending alignment with regulatory authorities, this 35-valent adult vaccine candidate is projected to enter clinical development by the end of 2026.