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Vaxcyte has advanced to the Phase II trial’s second and final stage (Stage 2) assessing its 31-valent pneumococcal conjugate vaccine (PCV) candidate, VAX-31 with the first subjects now dosed in this stage.
This follows a blinded review of the stage one tolerability and safety data, adhering to the study protocol.
Tailored to prevent invasive pneumococcal disease (IPD), VAX-31’s safety, tolerability, and immunogenicity are being assessed in this trial on healthy infants.
Vaxcyte anticipates sharing topline data from the trial’s primary three-dose immunisation series in mid-2026.
Vaxcyte co-founder and CEO Grant Pickering said: “Advancing to stage two 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.”
The randomised, double-blind, active-controlled Phase II study compared the vaccine’s tolerability, immunogenicity, and safety against Prevnar 20 (PCV20) in healthy infants.
In Stage 1, the tolerability and safety of the vaccine were assessed following the initial vaccination at various dosage levels of low, middle, and high in 48 infant subjects.
These received either VAX-31 or PCV20. Subjects who received VAX-31 in the first stage will proceed with the standard dosing regimen in the final stage.
The ongoing stage two aims to assess VAX-31 at the same dosing levels in nearly 750 infants, comparing it against PCV20.
The trial’s design, which includes a primary immunisation series, is aligned with recommendations from the Advisory Committee on Immunization Practices (ACIP). The series comprises three doses administered at two, four, and six months of age, followed by a booster dose at 12-15 months.
Prespecified immunogenicity endpoints of the study will focus on immune responses to both common and distinct serotypes in VAX-31, compared to PCV20.
Immune responses following the primary series (post-dose 3 or PD3) will be assessed by measuring serotype-specific immunoglobulin G (IgG) seroconversion rates, which is the proportion of subjects achieving the accepted IgG threshold of ≥0.35mcg/mL at 30 days PD3.
Additionally, IgG geometric mean titers will be measured at both 30 days PD3 and post-dose 4 (PD4), alongside other immunogenicity endpoints.
Safety evaluations will continue for six months post-booster across all study subjects. The trial is being conducted at around 50 sites in the US.
In September 2022, the company concluded subject enrolment in the Phase II trial of VAX-24, in healthy adults aged 65 years and above for IPD prevention.