Journal Article

High SARS-CoV-2 seroprevalence in children and adults in the Austrian ski resort of Ischgl

Rössler, Annika, Riepler, Lydia, Schips, Marta, Pipperger, Lisa, Binder, Sebastian C, Ranjan, Mrinalini, Falkensammer, Barbara, Borena, Wegene, von Laer, Dorothee, Kimpel, Janine, Walser, Andreas, Ulmer, Hanno, Knabl, Ludwig, Bandyopadhyay, Arnab, Meyer-Hermann, Michael, Volland, André, Mitra, Tanmay, Bates, Katie

2021

Overview

BackgroundIn early March 2020, a SARS-CoV-2 outbreak in the ski resort Ischgl in Austria initiated the spread of SARS-CoV-2 throughout Austria and Northern Europe.MethodsBetween April 21st and 27th 2020, a cross-sectional epidemiologic study targeting the full population of Ischgl (n = 1867), of which 79% could be included (n = 1473, incl. 214 children), was performed. For each individual, the study involved a SARS-CoV-2 PCR, antibody testing and structured questionnaires. A mathematical model was used to help understand the influence of the determined seroprevalence on virus transmission.ResultsThe seroprevalence was 42.4% (95% confidence interval (CI) 39.8–44.7). Individuals under 18 showed a significantly lower seroprevalence of 27.1% (95% CI 21.3-33.6) than adults (45%; 95% CI 42.2–47.7; OR of 0.455, 95% CI 0.356–0.682, p < 0.001). Of the seropositive individuals, 83.7% had not been diagnosed to have had SARS-CoV-2 infection previously. The clinical course was generally mild. Over the previous two months, two COVID-19-related deaths had been recorded, corresponding to an infection fatality rate of 0.25% (95% CI 0.03–0.91). Only 8 (0.5 %) individuals were newly diagnosed to be infected with SARS-CoV-2 during this study.ConclusionsIschgl was hit early and hard by SARS-CoV-2 leading to a high local seroprevalence of 42.4%, which was lower in individuals below the age of 18 than in adults. Mathematical modeling suggests that a drastic decline of newly infected individuals in Ischgl by the end of April occurred due to the dual impact from the non-pharmacological interventions and a high immunization of the Ischgl population.Plain Language SummaryThe Austrian ski resort of Ischgl was a major hot-spot of SARS-CoV-2 infection early on in the pandemic. Here, we investigated the number of people that had been previously infected with the virus in Ischgl in April 2020, by measuring antibodies, blood proteins produced in response to the virus, against SARS-CoV-2. We found that these antibodies were present in 42.4% of the individuals tested and that the majority of these infections, which were generally mild, had not been previously detected. Children were less likely to have these antibodies compared to adults. Using mathematical models, we also found that the subsequent decline in SARS-CoV-2 infections was likely caused by a combination of immunity in the population of Ischgl and of non-pharmaceutical interventions. Our findings allow a better understanding of localised outbreaks of SARS-CoV-2 and how these might be controlled in future.

• Publisher: Springer Nature B.V
• Subject: Age / Antibodies / Coronaviruses / COVID-19 / Disease transmission / Fatalities / Hospitalization / Households / Immunoassay / Laboratories / Non-pharmacological intervention / Population / Proteins / Self report / Serology / Severe acute respiratory syndrome coronavirus 2