Optimizing adult pneumococcal vaccination in India: Evidence from serotype surveillance

Introduction: Pneumococcal disease, caused by Streptococcus pneumoniae , is a major public health burden with high morbidity and mortality across all age groups in India. Limited adult pneumococcal vaccination policies, evolving serotype patterns, and delayed herd protection from paediatric immunization continue to challenge effective prevention of pneumococcal disease in adults. Methods: This retrospective laboratory surveillance study includes Streptococcus pneumoniae isolates from adults (>18 years) collected between January 2018 and May 2025 at Christian Medical College, Vellore and were serotyped using the Quellung and co-agglutination method. Percentage of serotype coverage for PCV20, PCV21, and PPSV23 was analysed. Results: Among 1,065 adult pneumococcal isolates, PCV20 covers 66.5% of invasive pneumococcal disease (IPD) serotypes, including emerging serotypes such as 15B and 11A, while PCV21 aligns poorly with the local epidemiology, covering only 46.5% of adult IPD serotypes. PPSV23 offers limited additional relevant serotype coverage beyond PCV20 and is limited by lower immunogenicity and hyporesponsiveness to multiple doses. Discussion: Our findings highlight significant gaps between the circulating serotypes in adults in India and those covered by current vaccines. PCV20 shows promise for broader adult protection; however, further multi-centre studies, cost-effectiveness analyses, and enhanced surveillance are needed to inform policy and optimize immunization strategies in resource-limited settings.