biostudies-literatureUnknown23(2)Regan AK<h4>Background</h4>Although several studies have reported attenuated influenza illness following influenza vaccination, results have been inconsistent and have focused predominantly on adults in the USA. This study aimed to evaluate the severity of influenza illness by vaccination status in a broad range of influenza vaccine target groups across multiple South American countries.<h4>Methods</h4>We analysed data from four South American countries (Argentina, Brazil, Chile, and Paraguay) participating in REVELAC-i, a multicentre, test-negative design, vaccine effectiveness network including 41 sentinel hospitals. Individuals hospitalised at one of these centres with severe acute respiratory infection were tested for influenza by real-time RT-PCR, and were included in the analysis if they hadThe Lancet. Infectious diseases222-232https://www.ebi.ac.uk/biostudies/studies/S-EPMC9876808biostudies-literatureSeverity of influenza illness by seasonal influenza vaccination status among hospitalised patients in four South American countries, 2013-19: a surveillance-based cohort study.PMC9876808Battaglia Paredes SCda Silva DAvon Horoch MCouto PRopero AMRegan AKda Silva ETGiovacchini CMDuca LVergara NBrstilo IFAvendano Vigueras MADel Valle Juarez MLoayza SGonzalez Caro CIKatz NAzziz-Baumgartner EAntman JOlivares MFAraya Sde Almeida WAFSotomayor VArriola CSFasce RBustos PNogareda FFandino MEfalseSeverity of influenza illness by seasonal influenza vaccination status among hospitalised patients in four South American countries, 2013-19: a surveillance-based cohort study.<h4>Background</h4>Although several studies have reported attenuated influenza illness following influenza vaccination, results have been inconsistent and have focused predominantly on adults in the USA. This study aimed to evaluate the severity of influenza illness by vaccination status in a broad range of influenza vaccine target groups across multiple South American countries.<h4>Methods</h4>We analysed data from four South American countries (Argentina, Brazil, Chile, and Paraguay) participating in REVELAC-i, a multicentre, test-negative design, vaccine effectiveness network including 41 sentinel hospitals. Individuals hospitalised at one of these centres with severe acute respiratory infection were tested for influenza by real-time RT-PCR, and were included in the analysis if they had2023-01-01T00:00:00Z2023 Feb2025-04-19T17:56:16.496Z2025-04-19T17:56:16.496ZS-EPMC98768083620679010.1016/S1473-3099(22)00493-5