Safety and Immunogenicity of SII’s 10-Valent Pneumococcal Conjugate Vaccine (PCV10-SII) in Vietnamese Children Aged from 6 Weeks to 24 Months: An Open-Label, Single-Arm Bridging Study

Background: Pneumococcal conjugate vaccines (PCVs) prevent severe disease in children, but high costs limit access. PNEUMOSIL®, a 10-valent PCV prequalified by World Health Organization (WHO) in 2019, offers a cost-effective alternative. This study assessed its safety and immunogenicity in Vietnamese children aged 6 weeks–24 months. Methods: An open-label, single-arm study enrolled 304 children in three age groups: 6 weeks–6 months (n=151), >6–12 months (n=76), and >12–24 months (n=77). Participants received two or three doses. Safety was evaluated through immediate reactions, adverse events (AEs), serious adverse events (SAEs), and withdrawals. Immunogenicity was measured 28 days after the final dose using serotype-specific IgG geometric mean concentrations (GMCs), opsonophagocytic activity (OPA) titers, and seroresponse rates. The trial was approved by the IRB of the National Ethics Council (code: No. 75/CN-HĐĐĐ on date June 4th, 2021) and was registered with ClinicalTrials.gov, NCT05140720. Results: Of 304 enrolled participants, 294 (96.7%) completed follow-up. No immediate adverse events or serious adverse events occurred. Unsolicited adverse events were reported in 17%, mainly respiratory, while serious adverse events occurred in 4%. Mild local/systemic reactions (e.g., injection site pain, crying) resolved without sequelae. Immunogenicity was strong, with GMCs 1.8–9.11 µg/mL, GMTs 277.8–22,342, and >90% achieving seroresponse for all 10 serotypes. Conclusions: PNEUMOSIL® demonstrated favorable safety and robust immunogenicity, supporting its inclusion in national immunization programs as an affordable option for pneumococcal disease prevention.