A 24-valent pneumococcal conjugate vaccine passes early safety and immunogenicity tests

Design

Two single-centre, randomised, double-blind phase 1 and 2 trials

Population

1,232 healthy Chinese adults aged 18 and over

Primary outcome

Adverse events and IgG seroconversion

Effect

High dose non-inferior to PPSV23 for seroconversion across all 24 serotypes; no vaccine-related serious events

Two single-centre, double-blind phase 1 and 2 trials in China enrolled 1,232 adults aged 18 and over. Phase 1 compared low- and high-dose PCV24 with the 23-valent polysaccharide vaccine (PPSV23) and placebo; phase 2 compared three PCV24 formulations with PPSV23.

Reactions were mainly grade 1 or 2, with rare grade 3 events in the first week and no vaccine-related serious adverse events over six months. The high-dose formulation met non-inferiority criteria for IgG seroconversion against PPSV23 for all 24 serotypes.

These are early-phase immunogenicity data in one country. They show the vaccine provokes antibodies safely, not that it prevents pneumococcal disease. Efficacy and comparisons with existing conjugate vaccines remain to be done.

• This is a phase 1 and 2 immunogenicity result; it does not change pneumococcal vaccine schedules.
• Antibody response is a surrogate; protection against invasive disease has not been measured.
• Continue using currently licensed pneumococcal vaccines according to national recommendations.
• Broader-valency conjugate vaccines aim to cover serotypes left by current vaccines.

Why it matters

Serotype replacement erodes current vaccines, and broader conjugates are the response.

Don't overread it

Phase 2 antibody data cannot show protection against pneumonia or invasive disease.

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