We conducted a multicentre hospital-based test-negative case-control study to measure the effectiveness of adapted bivalent COVID-19 mRNA vaccines against PCR-confirmed SARS-CoV-2 infection during the Omicron XBB lineage-predominant period in patients aged ≥ 60 years with severe acute respiratory infection from five countries in Europe. Bivalent vaccines provided short-term additional protection compared with those vaccinated > 6 months before the campaign: from 80% (95% CI: 50 to 94) for 14-89 days post-vaccination, 15% (95% CI: -12 to 35) at 90-179 days, and lower to no effect thereafter.

Cantacuzino National Military Medical Institute for Research and Development Bucharest Romania

CIBER Epidemiología y Salud Pública Madrid Spain

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

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 Centre for Microbiology Institute of Health Carlos 3 Madrid Spain

National Influenza Centre Laboratory of Viral Diseases Sciensano Brussels Belgium

National Institute of Public Health National Centre for Communicable Diseases Surveillance and Control Bucharest Romania

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

National Reference Centre for Influenza Robert Koch Institute Berlin Germany

Service Epidemiology of Infectious Diseases Sciensano Brussels Belgium

University Hospital Brno Masaryk University Brno Czechia

University Hospital Centre Split Split Croatia

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Early COVID-19 XBB.1.5 Vaccine Effectiveness Against Hospitalisation Among Adults Targeted for Vaccination, VEBIS Hospital Network, Europe, October 2023-January 2024