The vaccine is specifically designed to provide broad coverage against IPD, targeting approximately 94% of cases in US children under five years old. Credit: Gorodenkoff/Shutterstock.

Vaxcyte has commenced the Phase II trial of its 31-valent pneumococcal conjugate vaccine (PCV) candidate, VAX-31, in healthy infants, with the first subjects receiving the dose.

The study aims to assess the vaccine’s tolerability, immunogenicity, and safety in preventing invasive pneumococcal disease (IPD).

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Topline data from the primary three-dose immunisation series is expected by mid-2026, with further data from the booster dose to follow nine months later.

Vaxcyte is also set to announce topline data from the VAX-24 Phase II infant study by the end of the first quarter of 2025.

The vaccine is specifically designed to provide broad coverage against IPD, targeting approximately 94% of cases in US children under five years old.

The randomised, active controlled, double-blind, dose-finding VAX-31 Phase II infant study is conducted in two stages. It is being conducted at approximately 50 sites across the US.

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Stage one focuses on the tolerability and safety of three different dose levels of the vaccine, compared to PCV20, in approximately 48 infants using a dose-escalation methodology.

Following stage one, subjects will continue with the standard dosing regimen in stage two, which will expand to include nearly 750 infants.

The study’s design aligns with the ‘Advisory Committee on Immunization Practices’ (ACIP) recommendations, featuring a primary immunisation series at two, four, and six months old, and a booster dose at 12-15 months.

Key immunogenicity endpoints for the VAX-31 trial include comparing the immune responses across the different dose levels with PCV20 for both common and unique serotypes.

These will be measured based on serotype-specific immunoglobulin G seroresponse rates and geometric mean titers 30 days after the third dose and post-booster.

Safety evaluations will continue for six months after the booster dose.

Vaxcyte CEO and co-founder Grant Pickering said: “The initiation of the VAX-31 Phase II infant study marks a significant milestone as we continue advancing our PCV clinical programs, which also include the fully enrolled, ongoing VAX-24 Phase II infant study.

“PCVs are vital to combating Streptococcus pneumoniae, a serious public health threat exacerbated by increasing antimicrobial resistance.”

In September 2022, the company concluded subject enrolment in a Phase II clinical trial of the investigational vaccine, VAX-24.