Pfizer recently announced data from its phase 2 study (NCT06524414) evaluating the safety, tolerability and immunogenicity of a four-dose series of its investigational 25-valent pneumococcal conjugate vaccine candidate PF-07872412 (25vPnC) in infants compared to four doses of PREVNAR 20 at months 2, 4, 6 and 12-15. Based on the strong immune responses observed for all 25vPnC serotypes from phase 2, compared to PREVNAR 20, Pfizer is confident that the required non-inferiority thresholds may be achieved for the 25vPnG pediatric phase 3 program.

Key preliminary data from the broader phase 2 study were presented in an oral presentation at the 14th meeting of the International Society of Pneumonia and Pneumococcal Diseases in Copenhagen, Denmark (ISPPD). Results found that 1 month after dose 3, geometric mean titers for serotype 3 were 8.8-fold higher with 25vPnC than with PREVNAR 20 (4.22 vs. 0.48); 1 month after dose 4, geometric mean titers for serotype 3 were approximately 15-fold higher with 25vPnC than with Prevnar 20 (13.85 vs. 0.92). This vaccine candidate is expected to cover up to 90 percent of disease-causing serotypes in children under 5 years of age, which includes approximately 15 percent from serotype 3.

Annaliesa Anderson, PhD, Senior Vice President and Chief Vaccines Officer, Pfizer, said, “For more than 25 years, our vaccines have helped protect children from pneumococcal disease, yet significant disease burden remains. 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 program with the goal of delivering broader and more durable protection for children.”

The phase 2 study is a randomised trial in healthy infants, with initial enrolment beginning in July 2024, evaluating 25vPnC compared with PREVNAR 20. Participants were randomised to receive 25vPnC or PREVNAR 20 at months 2, 4, 6 and 12-15 assessing the safety and tolerability, including local and systemic reactogenicity within seven days after each vaccination, as well as Adverse Events (AEs) and serious AEs in participants who receive at least 1 dose. The trial also assessed immunogenicity 1 month after dose 3 and 1 month after dose 4, compared to 1 month after dose 3 and dose 4 with PREVNAR 20.

The safety and tolerability profile of 25vPnC was consistent with the currently approved and available pneumococcal vaccine. The most common local reactions were redness, swelling or pain at injection site similar to existing vaccines.

Despite significant reduction in pneumococcal disease burden by the currently available 20-valent standard-of-care-vaccine, serotype 3 remains a notable cause of invasive pneumococcal disease and complicated pneumonia in children. Therefore, based on this phase 2 data and discussions with regulatory authorities, Pfizer began a pivotal pediatric phase 3 program in May 2026. The studies evaluate safety, tolerability and immunogenicity of 25vPnC in healthy children where participants receive either 25vPnC or PCV20 at 2, 4, 6 and 12 to 15 months of age. Participants will receive the same vaccine for all four vaccinations for up to 2,400 individuals comparing 25vPnC to the currently licensed 20-valent standard-of-care vaccine.

The vaccine candidate covers 25 serotypes including serotype 3, adding 5 new serotypes to the established vaccine coverage for infants. If successful, this has the potential to broaden protection to about 90 percent of disease-causing serotypes in US children.

Meanwhile, as the strongest opportunity to maintain the company’s current leadership in the adult market over the long term, Pfizer has decided to move directly to a fifth-generation vaccine candidate covering 35 serotypes. This fifth-generation adult candidate has the potential to increase serotype coverage while also improving immunogenicity for critical serotypes including serotype 3 with Pfizer’s proprietary next-generation technology. The adult vaccine candidate is expected to enter clinical development by the end of 2026, pending alignment with regulatory authorities.