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

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

doi:10.1038/s43856-021-00007-1

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

Commun Med (Lond). 2021;1(1):4. doi: 10.1038/s43856-021-00007-1. Epub 2021 Jun 30.

Authors

Ludwig Knabl^#¹, Tanmay Mitra^#², Janine Kimpel^#¹, Annika Rössler¹, André Volland¹, Andreas Walser³, Hanno Ulmer⁴, Lisa Pipperger¹, Sebastian C Binder², Lydia Riepler¹, Katie Bates⁴, Arnab Bandyopadhyay², Marta Schips², Mrinalini Ranjan^{2

5}, Barbara Falkensammer¹, Wegene Borena¹, Michael Meyer-Hermann^{2

6}, Dorothee von Laer¹

Affiliations

¹ Institute of Virology, Department of Hygiene, Microbiology and Public Health, Medical University of Innsbruck, Innsbruck, Austria.
² Department of Systems Immunology and Braunschweig Integrated Centre of Systems Biology, Helmholtz Centre for Infection Research, Braunschweig, Germany.
³ Dr. Walser's surgery, Ischgl, Austria.
⁴ Department of Medical Statistics, Informatics and Health Economics, Medical University of Innsbruck, Innsbruck, Austria.
⁵ Centre for Mind/Brain Sciences, University of Trento, Trento, Italy.
⁶ Institute for Biochemistry, Biotechnology and Bioinformatics, Technische Universität Braunschweig, Braunschweig, Germany.

^# Contributed equally.

Abstract

Background: In 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.

Methods: Between April 21^st and 27^th 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.

Results: The 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.

Conclusions: Ischgl 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.

Keywords: SARS virus; Viral epidemiology; Viral infection.