SARS-CoV-2 Omicron XBB infections boost cross-variant neutralizing antibodies, potentially explaining the observed delay of the JN.1 wave in some Brazilian regions

Objectives The SARS-CoV-2 JN.1 lineage emerged in late 2023 and quickly replaced the XBB lineages, becoming the predominant Omicron variant worldwide in 2024. We estimate the epidemiological impact of this SARS-CoV-2 lineage replacement in Brazil and we further assessed the cross-reactive neutralizing antibody (NAb) responses in a cohort of convalescent Brazilian patients infected during 2023. Methods We analyzed the evolution of SARS-CoV-2 lineages and severe acute respiratory infection (SARI) cases in Brazil between July 2023 and March 2024. We evaluated the cross-reactive NAb responses to the JN.1 variant in a cohort of convalescent Brazilian patients, both before and after infection with XBB.1* lineages. Results JN.1 replaced XBB with similar temporal dynamics across all country regions, though its epidemiological impact varied between locations. The Southeastern, Southern, and Central-Western regions experienced a brief XBB wave around October 2023, shortly before the introduction of JN.1, without any immediate upsurge of SARI cases during viral lineage replacement. By contrast, the Northeastern and Northern regions did not experience an XBB wave in the latter half of 2023 and displayed a rapid surge in SARI cases driven by the emergence of the JN.1. We found that recent XBB infections in the Brazilian population significantly boosted cross-reactive NAb levels against JN.1. Conclusions The XBB wave observed in the second half of 2023 in some Brazilian states likely acted as a booster for population immunity, providing short-term protection against JN.1 infections and delaying the rise of SARI cases in certain regions of the country.