Influenza A viruses circulated in Europe from September 2023 to January 2024, with influenza A(H1N1)pdm09 predominance. We provide interim 2023/24 influenza vaccine effectiveness (IVE) estimates from two European studies, covering 10 countries across primary care (EU-PC) and hospital (EU-H) settings. Interim IVE was higher against A(H1N1)pdm09 than A(H3N2): EU-PC influenza A(H1N1)pdm09 IVE was 53% (95% CI: 41 to 63) and 30% (95% CI: -3 to 54) against influenza A(H3N2). For EU-H, these were 44% (95% CI: 30 to 55) and 14% (95% CI: -32 to 43), respectively.

Cantacuzino National Military Medical Institute for Research and Development Bucharest Romania

Centre National de Référence Virus des Infections Respiratoire Institut Pasteur Université Paris Cité Paris France

CIBER de Epidemiología y Salud Pública Institute of Health Carlos 3 Madrid Spain

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

Croatian Institute of Public Health Zagreb Croatia

Department for Infectious Disease Epidemiology Respiratory Infections Unit Robert Koch Institute Berlin Germany

Department of Child and Adolescent Health Mater Dei Hospital Msida Malta

Department of Infectious Diseases CHU UCL Namur Université catholique de Louvain Yvoir Belgium

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

Epiconcept Paris France

Epidemiology Department Instituto Nacional de Saúde Doutor Ricardo Jorge Lisbon Portugal

European Centre for Disease Prevention and Control Stockholm Sweden

HSE Health Protection Surveillance Centre Dublin Ireland

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

Instituto de Salud Pública de Navarra IdiSNA CIBERESP Pamplona Spain

Laboratório Nacional Referência Gripe e outros Vírus Respiratórios Instituto Nacional de Saúde Doutor Ricardo Jorge Lisbon Portugal

National Centre for Epidemiology Institute of Health Carlos 3 Madrid Spain

National Centre for Microbiology National Influenza Reference Laboratory WHO National Influenza Centre Institute of Health Carlos 3 Madrid Spain

National Institute for Public Health and the Environment Centre for Infectious Diseases Control Bilthoven the Netherlands

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

National Reference Centre for Influenza Robert Koch Institute Berlin Germany

National Virus Reference Laboratory University College Dublin Dublin Ireland

Nivel Utrecht the Netherlands

Public Health Agency of Sweden Stockholm Sweden

Servicio de vigilancia y control epidemiológico Subdirección general de Epidemiología y Vigilancia de la Salud Dirección General de Salud pública Valencia Spain

Servicio de Vigilancia y Salud Laboral Dirección General de Salud Pública y Ordenación Farmacéutica Consejería de Salud y Consumo Andalucía Spain

Sorbonne Université INSERM Institut Pierre Louis d'épidémiologie et de Santé Publique Paris France

University Hospital Brno and Masaryk University Brno Czechia

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