Immunogenicity and Safety of a Single Booster Dose of Sabin-Strain Inactivated Poliovirus Vaccine in Adolescents and Adults: A Phase IV, Open-Label Trial

Background: In China, the current national immunisation schedule extends only to 4 years of age, and no polio booster dose is recommended for adolescents or adults, with data on immunogenicity and safety in these populations lacking. This phase IV trial evaluated the immunogenicity and safety of a single booster dose of Sabin-strain inactivated poliovirus vaccine (sIPV) in Chinese adolescents and adults. Methods: This phase IV, open-label trial enrolled 120 healthy participants, comprising 60 adolescents aged 7–17 years and 60 adults aged 18–50 years, who received a single booster dose of sIPV. Participants were enrolled and vaccinated in Gansu Province, China, between 21 October and 1 November 2025. Immunogenicity was assessed by neutralising antibody titres against poliovirus types 1, 2, and 3 before and 30 days post-vaccination. Safety was evaluated through monitoring of adverse events throughout the 30-day follow-up period. Results: Following a single sIPV booster dose, seropositivity rates reached 100% for all three poliovirus serotypes in both age groups. Post-vaccination geometric mean titres (GMTs) for types 1, 2, and 3 were 1748.29, 3961.77, and 2089.08 in adolescents, and 1902.58, 4434.39, and 2256.16 in adults, respectively, with no significant between-group differences. Seroconversion rates for type 3 were significantly higher in adults than in adolescents (98.33% vs. 86.67%, p = 0.032). Geometric mean increases (GMIs) were significantly higher in adults for type 1 (72.12 vs. 28.10, p = 0.008) and type 3 (316.14 vs. 45.56, p < 0.001). The vaccine was well tolerated; vaccine-related adverse events were reported in 17.50% of participants, all mild to moderate, with no vaccine-related serious adverse events. Conclusions: A single booster dose of sIPV induced robust neutralising antibody responses across all three poliovirus serotypes in both adolescents and adults, with a favourable safety profile. Adults with lower baseline immunity derived proportionally greater fold-increases in antibody titres.