Safety and immunogenicity of the 24-valent pneumococcal conjugate vaccine in healthy Chinese adults: two single-center, randomized, double-blind Phase 1 and Phase 2 trials

Conventional pneumococcal vaccines cover limited serotypes. This study evaluated the safety and immunogenicity of 24-valent pneumococcal conjugate vaccine (PCV24) in Chinese adults aged ≥18 years. Two single-center, randomized, double-blind Phase 1/2 trials were conducted. Two hundred forty Phase 1 participants were randomized with an overall allocation ratio of 1:1:1:1 to low/high dose PCV24, 23-valent pneumococcal polysaccharide vaccine (PPSV23), or placebo. Nine hundred ninety‑two Phase 2 participants were randomized (1:1:1:1) to receive one of three PCV24 formulations (low-dose and low adjuvant, low-dose, high-dose) or PPSV23. Adverse events (AEs) within 30 days post-vaccination and study-wide serious adverse events (SAEs) were collected. Blood samples were tested for immunogenicity in Phase 2. Post-vaccination adverse reactions (ARs) within 0–30 days were primarily grade 1–2, with rare grade 3 events limited to the 0–7 days. No vaccine-related SAEs occurred over 6 months. Immunogenicity analysis confirmed that in all participants aged ≥18 years, the PCV24 high-dose group met non-inferiority criteria for IgG seroconversion of all 24 serotypes compared with PPSV23. The PCV24 vaccine exhibits a favorable safety profile and robust immunogenicity in Chinese adults aged ≥18 years, supporting further efficacy studies in larger populations. www.clinicaltrials.gov identifier: NCT07025876; NCT07035054.