IntroductionTwo large multicentre European hospital networks have estimated vaccine effectiveness (VE) against COVID-19 since 2021.AimWe aimed to measure VE against PCR-confirmed SARS-CoV-2 in hospitalised severe acute respiratory illness (SARI) patients ≥ 20 years, combining data from these networks during Alpha (March-June)- and Delta (June-December)-dominant periods, 2021.MethodsForty-six participating hospitals across 14 countries follow a similar generic protocol using the test-negative case-control design. We defined complete primary series vaccination (PSV) as two doses of a two-dose or one of a single-dose vaccine ≥ 14 days before onset.ResultsWe included 1,087 cases (538 controls) and 1,669 cases (1,442 controls) in the Alpha- and Delta-dominant periods, respectively. During the Alpha period, VE against hospitalisation with SARS-CoV2 for complete Comirnaty PSV was 85% (95% CI: 69-92) overall and 75% (95% CI: 42-90) in those aged ≥ 80 years. During the Delta period, among SARI patients ≥ 20 years with symptom onset ≥ 150 days from last PSV dose, VE for complete Comirnaty PSV was 54% (95% CI: 18-74). Among those receiving Comirnaty PSV and mRNA booster (any product) ≥ 150 days after last PSV dose, VE was 91% (95% CI: 57-98). In time-since-vaccination analysis, complete all-product PSV VE was > 90% in those with their last dose < 90 days before onset; ≥ 70% in those 90-179 days before onset.ConclusionsOur results from this EU multi-country hospital setting showed that VE for complete PSV alone was higher in the Alpha- than the Delta-dominant period, and addition of a first booster dose during the latter period increased VE to over 90%.

AP HP Hôpital Cochin Paris France

Cantacuzino National Military Medical Institute for Research Development Bucharest Romania

Carol Davila University of Medicine and Pharmacy Bucharest Romania

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

Centre Hospitalier de Luxembourg Luxembourg

Consortium for Biomedical Research in Epidemiology and Public Health Madrid Spain

Croatian Institute of Public Health Zagreb Croatia

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

Epiconcept Paris France

European Centre for Disease Prevention and Control Stockholm Sweden

Faculty of Medicine Masaryk University Brno Czechia

Faculty of Medicine University of Paris City Paris France

Grigore T Popa University of Medicine and Pharmacy Iasi Romania

Health Service Executive Health Protection Surveillance Centre Dublin Ireland

IDCU within Health promotion and disease prevention Directorate G'mangia Malta

Inserm CIC Cochin Pasteur Paris France

Instituto de Salud Pública de Navarra IdiSNA Pamplona Spain

Julius Center for Health Sciences and Primary Care University Medical Center Utrecht Utrecht the Netherlands

Lithuanian University of Health Sciences Kaunas Lithuania

Luxembourg Institute of Health Luxembourg

National Centre for Epidemiology Institute of Health Carlos 3 Madrid Spain

National Centre for Microbiology Institute of Health Carlos 3 Madrid Spain

National Institute of Health Dr Ricardo Jorge Lisbon Portugal

National Public Health Organisation Athens Greece

Robert Koch Institute Berlin Germany

Sciensano Brussels Belgium

Servicio de Epidemiología Dirección General de Salud Pública Consejería de Sanidad de Galicia Santiago de Compostela A Coruna Spain

Servicio de Medicina Preventiva Hospital Universitario Son Espases Servicio de Epidemiología Consellería de Salut Palma Spain

St Parascheva Clinical Hospital of Infectious Diseases Iasi Romania

Teaching Public Health Institute of Split Dalmatia County Split Croatia

Universitair Ziekenhuis Brussel Brussels Belgium

University Hospital Brno Brno Czechia

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