Long-term antibody trajectories after PPSV23 in elderly: Results from a 4-year follow-up study.

Background: The 23-valent pneumococcal polysaccharide vaccine (PPSV23) is recommended for standalone or sequential use in the elderly in many countries to prevent pneumococcal disease, making it crucial to assess vaccine response and long-term persistence.

Purpose: We aimed to describe the trajectories of circulating antibody levels to the PPSV23 in the elderly following immunization.

Methods: Eligible individuals aged 65 to 70 years were enrolled and vaccinated with one dose of PPSV23. Blood samples were collected at baseline (day 0), 4-6 weeks, one year, two years, three years, and four years after vaccination from November 2019 to December 2023. Serotype-specific IgG antibodies were measured for 7(4,6B,9 V,14,18C,19F and 23F) out of the 23 vaccine serotypes. Group-based trajectory modeling (GBTM) was applied to identify distinct trajectories of IgG concentration at each visit after immunization.

Results: A total of 237 participants completed all six visits over the four-year follow-up period, and the geometric mean concentrations (GMC) of antibodies against the seven serotypes remained elevated above the baseline levels by the fourth year. Females and those with a body mass index (BMI) over 25 have generally higher antibody levels pre- and post-immunization across the seven serotypes, with serotypes 6B, 18C show significant difference in higher BMI individuals, and serotype 9 V show significant difference in females after immunization. Based on GBTM, we identified two or three distinct trajectory types of IgG concentration changes across serotypes, with the exception of serotype 4, and we found that participants who showed a more rapid decline in antibody levels two years after vaccination had significantly higher baseline antibody levels.

Conclusion: Pneumococcal IgG antibody levels persist for a minimum of four years post-vaccination; Our findings indicate that BMI, gender, and pre-vaccination antibody concentrations should be considered when developing vaccination and revaccination strategies in the elderly.