Pneumococcal baseline IgG antibody levels and immune response to 23-valent pneumococcal polysaccharide vaccine among Indian adults.

Measuring immune responses to pneumococcal vaccines is crucial for evaluating their impact and efficacy. Herein, we measured type-specific IgG antibody levels before and after immunization with the 23-valent pneumococcal polysaccharide vaccine (PPSV23) in 51 healthy Indian adults using WHO-ELISA. Baseline geometric mean concentrations were adequate (≥1.3 μg/mL) against ∼83% of the capsule polysaccharide (CPS) types, with notably higher levels for serotypes 14, 15B, 19A, and 33F. Post-vaccination, IgG antibody levels significantly increased for 22 of 23 CPS types, with medians ranging from 2.3 to 57.8 μg/mL. The highest geometric mean fold rise (∼6 to 9-fold) was observed for CPS types 7F, 9N, 8, and 33F. The findings highlight the capability of PPSV23 to strengthen protective immunity against pneumococcal disease in Indian adults, advocating for its continued use. Further studies are needed to optimize vaccination strategies and evaluate the functional activity of induced antibodies.