Vaxcyte has commenced dosing in the second and final stage of its Phase II clinical trial evaluating VAX-31, marking a significant milestone in the development of what could be the broadest-spectrum pneumococcal conjugate vaccine (PCV) for infants to date.
The advancement follows a successful blinded review of Stage 1 safety and tolerability data, which evaluated the vaccine at low, middle, and high dose levels in 48 infant subjects. The ongoing Stage 2 will expand the study to approximately 750 infants, comparing VAX-31 against Prevnar 20 (PCV20).
"Advancing to Stage 2 of the VAX-31 infant Phase II study represents a significant step forward in evaluating the broadest vaccine candidate in the clinic today for this vulnerable population," said Grant Pickering, Chief Executive Officer and Co-Founder of Vaxcyte.
Comprehensive Trial Design and Endpoints
The randomized, double-blind, active-controlled study follows the Advisory Committee on Immunization Practices (ACIP) recommendations, implementing a primary immunization series of three doses at two, four, and six months of age, followed by a booster at 12-15 months.
Key immunogenicity endpoints will assess immune responses through:
- Serotype-specific immunoglobulin G (IgG) seroconversion rates
- IgG geometric mean titers at 30 days post-dose 3 and post-dose 4
- Safety evaluations continuing for six months post-booster
Potential Impact on Public Health
VAX-31 is designed to provide broader protection against both currently circulating and historically prevalent pneumococcal strains. The vaccine candidate shows promise in addressing:
- Approximately 94% of invasive pneumococcal disease cases
- About 93% of acute otitis media cases in U.S. children under five years
- Coverage of serotypes associated with antibiotic resistance and meningitis
Jim Wassil, Executive Vice President and Chief Operating Officer of Vaxcyte, emphasized the potential impact: "PCVs have demonstrated the ability to deliver herd immunity to protect against devastating diseases caused by Streptococcus pneumoniae bacteria, and our technology has the potential to deliver best-in-class PCVs with broader coverage for both infants and adults."
Development Timeline and Next Steps
The study is being conducted across approximately 50 U.S. sites. Vaxcyte anticipates:
- Topline data from the primary three-dose immunization series by mid-2026
- Booster dose results approximately nine months after the initial data
- Continued safety monitoring through six months post-booster for all participants
The FDA has already granted Breakthrough Therapy designation to VAX-31 for preventing invasive pneumococcal disease in adults, highlighting the vaccine's potential significance in addressing this serious public health concern.
