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

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BACKGROUNDPneumococcal 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.AIMWe 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).METHODSIn 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.RESULTSWe 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).CONCLUSIONSThe 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.

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