Vaxcyte Completes Enrollment for its Phase 1/2 Trial for Pneumococcal Vaccine VAX-31


Study will determine the effectiveness of vaccine in preventing invasive pneumococcal disease.

Nurse or doctor holding Pneumococcal Vaccine |Image Credits: Unsplash

Vaxcyte, a clinical-stage company that develops vaccines against bacterial diseases, recently announced the completion of enrollment for its phase 1/2 clinical trial. This study will assess VAX-31, a candidate for a 31-valent pneumococcal conjugate vaccine (PCV), aimed at preventing invasive pneumococcal disease (IPD). Vaxcyte anticipates releasing primary data concerning the safety, tolerability, and immune response generated by the vaccine from this study in the third quarter of 2024.

The VAX-31 phase 1/2 clinical study is a randomized, observer-blind, active-controlled, dose-finding study involving 1,015 participants. The study compares three different dosage levels of VAX-31 (low, middle, and high) against Prevnar 20 (PCV20). The goal of this study is to determine the optimal dosage of VAX-31 while ensuring its safety and effectiveness.

“Vaxcyte aims to efficiently create and deliver high-fidelity, broad-spectrum carrier-sparing conjugate vaccines in order to add coverage without compromising overall immune responses by using modern synthetic techniques, including advanced chemistry and the XpressCF cell-free protein synthesis platform,” according to Vaxcyte statement. “Vaxcyte is deploying this approach with VAX-24 and VAX-31, the latter of which has the potential to provide the broadest coverage of any PCV to reach the clinic with approximately 95% coverage of circulating IPD strains in the US adult population.”1

In the initial phase 1 segment of the study, 64 healthy adults aged 50 to 64 received a single injection of VAX-31 at 1 of the 3 dosages, which was then compared to PCV20. This phase focused primarily on evaluating the safety and tolerability of the vaccine. An independent Data Monitoring Committee reviewed these results and endorsed the continuation of the study into phase 2. Participants from phase 1 will also have their immunogenicity assessed, and these findings will be combined with data from phase 2 participants.

Phase 2 involves 951 adults aged 50 and older, who will also receive a single injection of VAX-31 at the same 3 dose levels for comparative analysis against PCV20. This phase aims to evaluate not only the safety and tolerability but also the immunogenicity of VAX-31, focusing on the induction of antibody responses. The study, conducted across approximately 25 sites in the US, will monitor the participants for safety for 6 months post-vaccination.

Main Takeaways

  1. Vaxcyte is at the forefront of developing advanced pneumococcal vaccines, with two key candidates: VAX-31 and VAX-24. VAX-31, a 31-valent PCV, is currently in a Phase 1/2 clinical trial.
  2. Vaxcyte employs modern synthetic techniques and a novel cell-free protein synthesis platform, XpressCF, for developing its vaccines.
  3. The company's innovative approach and promising clinical trial results have garnered recognition, such as the FDA's Breakthrough Therapy designation for VAX-24 for the prevention of IPD in adults.

According to the Centers for Disease Control and Prevention (CDC), IPD refers to any infection caused by bacteria called Streptococcus pneumoniae, or pneumococcus. Pneumococcal infections can range from ear and sinus infections to pneumonia and bloodstream infections. There are Food and Drug Administration (FDA)-approved vaccines to help prevent pneumococcal disease.2

Based upon the successful results, in January 2023, Vaxcyte revealed that the FDA had awarded the breakthrough therapy designation to VAX-24, similar to VAX-31, for the prevention of IPD in adults. This decision was based on encouraging topline outcomes from the phase 1/2 proof-of-concept study. The study assessed VAX-24's safety, tolerability, and immunogenicity in adults aged 18 to 64 years. Developed on a novel cell-free protein synthesis platform, VAX-24 appeared in a December 2023 phase 1/2 trial as the first vaccine of its kind to target this many pneumococcal serotypes without a reduction in immunogenicity.

"VAX-24 is an improved PCV that for the first time, provides the ability to simultaneously achieve both higher serotype valency and enhanced immune response," said Vaxcyte Chief Operating Officer James Wassil, MS.3

Overall, Vaxcyte, has completed enrollment for its phase 1/2 trial of the VAX-31 PCV, aimed at preventing IPD. The study evaluates the efficacy and safety of VAX-31 compared to PCV20, focusing on identifying the optimal dosage. Outcomes are anticipated in Q3 2024, marking a step in Vaxcyte's strategy to protect against IPD.


  1. Inc V. Vaxcyte completes enrollment of phase 1/2 study evaluating vax-31 for the prevention of invasive pneumococcal disease (Ipd) in adults aged 50 and older. GlobeNewswire News Room. Published January 29, 2024. Accessed February 1, 2024.
  2. Pneumococcal disease. CDC. Published September 29, 2024. Accessed February 1, 2024.
  3. Bender K. Investigational pneumococcal vaccine broadens coverage without reducing immunogenicity. ContagionLive. Published December 18, 2023. Accessed February 1, 2024.
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