Anticipating impact of implementing PCV20 or PCV21 vaccines for older adults in the immunisation programme for invasive pneumococcal disease, using nationwide surveillance data, Israel, 2009 to 2024

BACKGROUND Pneumococcal conjugate vaccines (PCVs) have reduced vaccine-type (VT) invasive pneumococcal disease (IPD) in older adults through direct and indirect effects. However, non-vaccine-type serotypes have emerged. Since the recently licensed PCV20 and PCV21 vaccines differ in serotype composition, epidemiological data are essential to guide adult vaccination policy. AIM We aimed to assess serotype-specific IPD dynamics in older adults in Israel and evaluate the potential impact of implementing either the PCV20 or PCV21 vaccine in the adult National Immunisation Programme (NIP). METHODS In a national active IPD surveillance study in Israel, 2009–2024, on adults aged ≥ 65 years, IPD incidence per 100,000 population was assessed by age group, individual serotype and VT group. RESULTS We recorded 3,553 IPD episodes. All-IPD incidence was relatively stable between 2014/15 and 2023/24, excluding the COVID-19 period. In the late PCV13 period (2014–2019, 1,210 IPD episodes) and late/post COVID-19 pandemic (2021-2024, 608 episodes) periods, incidence of serotypes unique to PCV21 (VT21-only) was consistently higher than that of those unique to PCV20 (VT20-only). During 2022–2024, VT21-only IPD constituted 25.5% of all-IPD cases compared with 10.9% for VT20-only. Of the VT20-only serotypes, serotype 14 showed the highest late/post-pandemic incidence (1.76 per 100,000). CONCLUSIONS The PCV21 vaccine currently demonstrates broader serotype coverage than PCV20 among older adults in Israel. However, the spectrum of serotypes only partially overlap. Potential further serotype-specific dynamics following PCV20 implementation in the paediatric NIP and unknown actual effectiveness of newly introduced vaccine serotypes make it difficult to accurately predict impact following implementation.