We estimated the effectiveness of the adapted monovalent XBB.1.5 COVID-19 vaccines against PCR-confirmed SARS-CoV-2 hospitalisation during the BA.2.86/JN.1 lineage-predominant period using a multicentre test-negative case-control study in Europe. We included older adults (≥ 65 years) hospitalised with severe acute respiratory infection from November 2023 to May 2024. Vaccine effectiveness was 46% at 14-59 days and 34% at 60-119 days, with no effect thereafter. The XBB.1.5 COVID-19 vaccines conferred protection against BA.2.86 lineage hospitalisation in the first 4 months post-vaccination.

• Keywords
• case–control study, elderly, severe acute respiratory infections (SARI), test‐negative design, vaccine effectiveness,
• MeSH
• COVID-19 * prevention & control   epidemiology   virology   MeSH
• Hospitalization * statistics & numerical data   MeSH
• Humans MeSH
• SARS-CoV-2 * immunology   MeSH
• Aged, 80 and over MeSH
• Aged MeSH
• Case-Control Studies MeSH
• Vaccine Efficacy * MeSH
• COVID-19 Vaccines * immunology   administration & dosage   MeSH
• Check Tag
• Humans MeSH
• Male MeSH
• Aged, 80 and over MeSH
• Aged MeSH
• Female MeSH
• Publication type
• Journal Article MeSH
• Multicenter Study MeSH
• Research Support, Non-U.S. Gov't MeSH
• Geographicals
• Europe epidemiology   MeSH
• Names of Substances
• COVID-19 Vaccines * MeSH