biostudies-literatureBabouee Flury BSwiss National Science FoundationBundesamt für GesundheitHealth Department of the Canton of St. Gallene1004125https://www.ebi.ac.uk/biostudies/studies/S-EPMC9678290biostudies-literatureUnknown19(11)<h4>Background</h4>Knowledge about protection conferred by previous Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) infection and/or vaccination against emerging viral variants allows clinicians, epidemiologists, and health authorities to predict and reduce the future Coronavirus Disease 2019 (COVID-19) burden. We investigated the risk and symptoms of SARS-CoV-2 (re)infection and vaccine breakthrough infection during the Delta and Omicron waves, depending on baseline immune status and subsequent vaccinations.<h4>Methods and findings</h4>In this prospective, multicentre cohort performed between August 2020 and March 2022, we recruited hospital employees from ten acute/nonacute healthcare networks in Eastern/Northern Switzerland. We determined immune status in September 2021 basPLoS medicineRisk and symptoms of COVID-19 in health professionals according to baseline immune status and booster vaccination during the Delta and Omicron waves in Switzerland-A multicentre cohort study.PMC9678290PZ00P3_17991931CA30_19654420.008218/421-28/1Kahlert CRKohler PMeier Kleeb DBesold URisch LBrucher AWiggli BMcGeer AEgger TRieder PMoller JCRutti MFriedl ABabouee Flury BGusewell SSURPRISE Study GroupSchmid HRStocker RLemmenmeier EVuichard-Gysin DSchlegel MKuster SPLeal OfalseRisk and symptoms of COVID-19 in health professionals according to baseline immune status and booster vaccination during the Delta and Omicron waves in Switzerland-A multicentre cohort study.<h4>Background</h4>Knowledge about protection conferred by previous Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) infection and/or vaccination against emerging viral variants allows clinicians, epidemiologists, and health authorities to predict and reduce the future Coronavirus Disease 2019 (COVID-19) burden. We investigated the risk and symptoms of SARS-CoV-2 (re)infection and vaccine breakthrough infection during the Delta and Omicron waves, depending on baseline immune status and subsequent vaccinations.<h4>Methods and findings</h4>In this prospective, multicentre cohort performed between August 2020 and March 2022, we recruited hospital employees from ten acute/nonacute healthcare networks in Eastern/Northern Switzerland. We determined immune status in September 2021 bas2022-01-01T00:00:00Z2022 Nov2025-04-18T17:07:39.165Z2025-04-07T04:41:40.409ZS-EPMC96782903634295610.1371/journal.pmed.1004125