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Seroprevalence of SARS-CoV-2 infection in the Tyrolean district of Schwaz at the time of the rapid mass vaccination in March 2021 following B.1.351-variant outbreak.

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Willeit, Peter 
Kimpel, Janine 
Winner, Hannes 
Harthaller, Teresa 
Schäfer, Helena 


In order to curb the rapid dissemination of the B.1.351 variant of SARS-CoV-2 in the district of Schwaz and beyond, the EU allocated additional vaccine doses at the beginning of March 2021 to implement a rapid mass vaccination of the population (16+). The aim of our study was to determine the seroprevalence of SARS-CoV-2 among the adult population in the district of Schwaz at the time of the implementation. Data on previous history of infections, symptoms and immunization status were collected using a structured questionnaire. Blood samples were used to determine SARS-CoV-2 specific anti-spike, anti-nucleocapsid and neutralizing antibodies. We recruited 2,474 individuals with a median age (IQR) of 42 (31-54) years. Using the official data on distribution of age and sex, we found a standardized prevalence of undocumented infections at 15.0% (95% CI: 13.2-16.7). Taken together with the officially documented infections, we estimated that 24.0% (95% CI: 22.5-25.6) of the adult population had prior SARS-CoV-2 infection. Hence, the proportion of undocumented infections identified by our study was 55.8% (95% CI: 52.7-58.5). With a vaccination coverage of 10% among the adults population at that time, we imply that a minimum of two-thirds of the target popuation was susceptible to the circulating threat when this unique campaign started.


Peer reviewed: True

Acknowledgements: We thank Maria Huber, Albert Falch, Evelyn Peer, Lisa-Maria Raschbichler, and the whole diagnostic and research team at the Institute of Virology for excellent technical support. We are also grateful to Bianca Neurauter, Eva Hochmuth, and Luiza Hoch and the whole organization team for excellent coordination of the study both at the laboratory and at the study site.


Comirnaty, SARS-CoV-2, anti-N, beta, seropositivity, seroprevalence, undocumented infection, vaccination, Adult, Antibodies, Neutralizing, COVID-19, Disease Outbreaks, Humans, Mass Vaccination, SARS-CoV-2, Seroepidemiologic Studies, Viral Vaccines

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Front Public Health

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Frontiers Media SA