Epidemiological impact of a 20- or 21-valent pneumococcal conjugate vaccine in the Japan adult population: insights from a dynamic transmission model

BACKGROUND: This study assessed the public health impact of adult pneumococcal vaccination strategies in Japan, comparing 20-valent (PCV20) and 21-valent (V116) pneumococcal conjugate vaccines with the current 23-valent polysaccharide vaccine (PPSV23). METHODS: An age- and serotype-specific dynamic transmission model calibrated to Japanese data estimated reductions in invasive pneumococcal disease (IPD) across age and risk groups. All scenarios assumed pediatric introduction of PCV20. RESULTS: Under current adult recommendations (targeting 65-year-olds), switching adult vaccination to PCV20 yielded up to a 0.3% decrease in adult IPD versus PPSV23, while V116 yielded up to a 2.6% reduction. Expanding age- and risk-based recommendations (both in adults aged ≥ 65-years-old and the at-risk 15-64-year-old population) produced larger reductions: up to 0.9% with PCV20 and 3.8% with V116. Further gains were projected when expanded recommendations were combined with increased vaccination coverage (from 39.1% to 53.2%-93.8%), with IPD reductions of 2.6%-6.5% for PCV20 and 8.5%-18.2% for V116. CONCLUSIONS: Results highlight the value of broader age recommendations and higher vaccine uptake in Japan and indicate that V116 can achieve greater reductions in pneumococcal disease burden than PCV20 or PPSV23, supporting consideration of V116 for adult vaccination in Japan.