Estimation of preventable pneumococcal disease burden by PCV20 or PCV21 under the national immunization program for adults aged 65 years in Japan

Aims: To estimate the preventable pneumococcal disease burden by 21-valent pneumococcal conjugate vaccine (PCV21) compared to PCV20 for the national immunization program for adults aged 65 years or older in Japan. Methods: Serotype distribution among isolates and the annual incidence of invasive pneumococcal disease (IPD) in adults were monitored. The numbers of IPD or pneumococcal community-acquired pneumonia (pCAP) cases preventable by immunization with PCV20 or PCV21 were estimated according to reported vaccine efficacy and duration of protection in older adults. Data from our nationwide study of adult IPD surveillance and a multicenter study of pCAP were used. Results: The mean annual incidence of adult patients with IPD caused by all serotypes among adults aged [≥]65 years, which declined during the COVID-19 pandemic period, recovered to 89% of the pre-pandemic level in 2025. During 2023-2025, the proportion of PCV20-non-PCV21 serotypes was 8.5% for adults aged [≥]65 years. At the current vaccination coverage rate of 40%, the numbers of preventable IPD cases (per person per year) by PCV20 and PCV21 were 36 and 53, respectively. The preventable numbers of pCAP cases by PCV20 and PCV21 were 2,821 and 4,765, respectively. The estimated number of preventable pCAP cases was approximately 80-90 times higher than that of preventable IPD cases. Conclusion: Our data indicate that PCV21 could prevent 1.5-1.7 times as many pneumococcal disease cases as PCV20 among adults aged [≥] 65 years in Japan. However, PCV20 should be considered if the incidence of adult IPD cases caused by PCV20-non-PCV21 serotypes increases.