24-Valent Pneumococcal Conjugate Vaccine Shows Strong Immune Response in Infants

Positive topline results have been announced from a phase 2 trial evaluating the safety, tolerability and immunogenicity of a 24-valent pneumococcal conjugate vaccine candidate (VAX-24) for the prevention of invasive pneumococcal disease in healthy infants, biotechnology company Vaxcyte announced in a release.¹ The company said the data will be used as a basis for a potential phase 3 program.

“Despite current vaccination efforts, Streptococcus pneumoniae is the leading cause of vaccine-preventable deaths globally in children under five,” Jim Wassil, Executive Vice President and Chief Operating Officer of Vaxcyte, said in a release.¹ “[These] results reinforce our commitment to advancing the broadest-spectrum [pneumococcal conjugate vaccines] to address the substantial invasive pneumococcal disease burden in the infant population, helping to reduce transmission and strengthen community immunity against the consequences of this devastating bacteria.”

READ MORE: Pneumococcal Disease Concerns Remain Despite Successful Vaccine Introduction

The VAX-24 infant study (NCT05844423) is a randomized, observer-blind, active-controlled, dose-finding phase 2 trial evaluating the safety, tolerability and immunogenicity of VAX-24 in infants compared to 20-valnet pneumococcal conjugate vaccine (Prevnar 20). The study cohort includes 802 healthy infants who were aged between 42 and 89 days when enrolled. The study includes 4 arms: a low dose of VAX-24, a mid-dose of VAX-24, a mixed dose of VAX-24, and an active comparator of Prevnar 20.

Patients in the study received injections at 2, 4, 6 and between 12 to 15 months of age. The study found that all of the evaluated doses elicited substantial immunoglobulin G (IgG) and opsonophagocytic assay (OPA) immune responses at 1-month after the third dose. The mid-dose met the target precedent non-inferiority criteria on relative seroconversion rates and also met the target IgG Geometric Mean Ratio point estimate of greater than 0.6³ on all currently circulating serotypes contained in VAX-24 after the third dose.

Dose-dependent immune responses were consistently demonstrated at all doses with little to no carrier suppression. Additionally, the data showed the vaccine was well-tolerated and had a similar safety profile to Prevnar 20 across all doses.

Vaxcyte said in the release data for post-dose 4 booster is expected by the end of 2025 and that it anticipates topline data from the VAX-31 infant phase 2 study in mid-2026. The company also said that, depending on the data, it plans to initiate an infant phase 3 study with either VAX-24 or VAX-31.

“Based on the strength of these data, we have selected the mid-dose as the basis of an optimized dose formulation to advance VAX-24 and, pending the VAX-31 phase 2 dose-finding study topline data readout, plan to initiate a phase 3 infant program with either VAX-24 or VAX-31,” Grant Pickering, CEO and Co-Founder of Vaxcyte, said in a release. “These results affirm the potential of our carrier-sparing platform to add coverage and maintain robust immune responses, reinforcing our confidence as we advance our PCVs into adult and infant Phase 3 programs.”

READ MORE: Pneumococcal Resource Center

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References

1. Vaxcyte Announces Positive Topline Results from VAX-24 Infant Phase 2 Dose-Finding Study. News Release. Vaxcyte. March 31, 2025. Accessed April 8, 2025. https://investors.vaxcyte.com/news-releases/news-release-details/vaxcyte-announces-positive-topline-results-vax-24-infant-phase-2