We conducted a multicentre test-negative case-control study covering the period from October 2023 to January 2024 among adult patients aged ≥ 18 years hospitalised with severe acute respiratory infection in Europe. We provide early estimates of the effectiveness of the newly adapted XBB.1.5 COVID-19 vaccines against PCR-confirmed SARS-CoV-2 hospitalisation. Vaccine effectiveness was 49% overall, ranging between 69% at 14-29 days and 40% at 60-105 days post vaccination. The adapted XBB.1.5 COVID-19 vaccines conferred protection against COVID-19 hospitalisation in the first 3.5 months post vaccination, with VE > 70% in older adults (≥ 65 years) up to 1 month post vaccination.

Cantacuzino National Military Medical Institute for Research and Development Bucharest Romania

Clinic of Infectious Diseases and Dermatovenerology Institute of Clinical Medicine Medical Faculty Vilnius University Vilnius Lithuania

Consortium for Biomedical Research in Epidemiology and Public Health Madrid Spain

Croatian Institute of Public Health Zagreb Croatia

Department for Infectious Disease Epidemiology Robert Koch Institute Berlin Germany

Department of Infectious Diseases Lithuanian University of Health Sciences Kaunas Lithuania

Department of Medical Microbiology and Infection Prevention and Control Ziekenhuisnetwerk Antwerpen Antwerp Belgium

Dr Victor Babes Clinical Hospital of Infectious and Tropical Diseases Bucharest Romania

Epidemiology Department Epiconcept Paris France

Epidemiology Department National Health Institute Doutor Ricardo Jorge Lisbon Portugal

European Centre for Disease Prevention and Control Stockholm Sweden

Health Service Executive Health Protection Surveillance Centre Dublin Ireland

Infectious Disease Prevention and Control Unit Health Promotion and Disease Prevention Msida Malta

Infectious Diseases Department National Health Institute Doutor Ricardo Jorge Lisbon Portugal

Instituto de Salud Pública de Navarra IdiSNA Pamplona Spain

National Centre for Epidemiology Institute of Health Carlos 3 Madrid Spain

National Laboratory for Health Security Epidemiology and Surveillance Centre Semmelweis University Budapest Hungary

National Reference Centre for Influenza Robert Koch Institute Berlin Germany

University Hospital Brno Masaryk University Brno Czechia

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