Mazagatos, ClaraDelgado-Sanz, ConcepcionMonge Corella, SusanaPozo Sanchez, FranciscoOliva, JesúsSandonis-Martin, VirginiaGandarillas, AnaQuiñones-Rubio, CarmenRuiz-Sopeña, CristinaGallardo-García, VirtudesBasile, LucaBarranco Boada, María IsabelHidalgo-Pardo, OlgaVazquez-Cancela, OlallaGarcía-Vázquez, MiriamFernández-Sierra, AmeliaMilagro-Beamonte, AnaOrdobás, MaríaMartínez-Ochoa, EvaFernández-Arribas, SocorroLorusso, NicolaMartínez, AnaGarcía-Fulgueiras, AnaSastre-Palou, BartoloméLosada-Castillo, IsabelMartínez-Cuenca, SilviaRodríguez-Del Águila, MarLatorre, MiriamLarrauri, AmparoSARI surveillance VE group in SpainCasas Flecha, InmaculadaVázquez-Morón, SoniaIglesias-Caballero, Maria2023-02-072023-02-072022-11Influenza Other Respir Viruses. 2022 Nov;16(6):1014-1025.http://hdl.handle.net/20.500.12105/15462Background: With the emergence of SARS-CoV-2, influenza surveillance systems in Spain were transformed into a new syndromic sentinel surveillance system. The Acute Respiratory Infection Surveillance System (SiVIRA in Spanish) is based on a sentinel network for acute respiratory infection (ARI) surveillance in primary care and a network of sentinel hospitals for severe ARI (SARI) surveillance in hospitals. Methods: Using a test-negative design and data from SARI admissions notified to SiVIRA between January 1 and October 3, 2021, we estimated COVID-19 vaccine effectiveness (VE) against hospitalization, by age group, vaccine type, time since vaccination, and SARS-CoV-2 variant. Results: VE was 89% (95% CI: 83-93) against COVID-19 hospitalization overall in persons aged 20 years and older. VE was higher for mRNA vaccines, and lower for those aged 80 years and older, with a decrease in protection beyond 3 months of completing vaccination, and a further decrease after 5 months. We found no differences between periods with circulation of Alpha or Delta SARS-CoV-2 variants, although variant-specific VE was slightly higher against Alpha. Conclusions: The SiVIRA sentinel hospital surveillance network in Spain was able to describe clinical and epidemiological characteristics of SARI hospitalizations and provide estimates of COVID-19 VE in the population under surveillance. Our estimates add to evidence of high effectiveness of mRNA vaccines against severe COVID-19 and waning of protection with time since vaccination in those aged 80 or older. No substantial differences were observed between SARS-CoV-2 variants (Alpha vs. Delta).engVoRhttp://creativecommons.org/licenses/by/4.0/COVID-19COVID-19 vaccineSARI surveillanceSARS-CoV-2SpainTest-negative designVaccine effectivenessCOVID-19Respiratory Tract InfectionsCOVID-19 VaccinesHospitalizationHumansSARS-CoV-2Sentinel SurveillanceSpainVaccine EfficacyAtribución 4.0 Internacional358804691661014-102510.1111/irv.130261750-2659Influenza and other respiratory virusesopen access