Follow-up study in the ski-resort Ischgl: Antibody and T cell responses to SARS-CoV-2 persisted for up to 8 months after infection and transmission of virus was low even during the second infection wave in Austria

  1. Wegene Borena
  2. Zoltán Bánki
  3. Katie Bates
  4. Hannes Winner
  5. Lydia Riepler
  6. Annika Rössler
  7. Lisa Pipperger
  8. Igor Theurl
  9. Barbara Falkensammer
  10. Hanno Ulmer
  11. Andreas Walser
  12. Daniel Pichler
  13. Matthias Baumgartner
  14. Sebastian Schönherr
  15. Lukas Forer
  16. Ludwig Knabl
  17. Reinhard Würzner
  18. Dorothee von Laer
  19. Jörg Paetzold
  20. Janine Kimpel
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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. In a cross-sectional study, we found that the seroprevalence in the adult population of Ischgl had reached 45% by the end of April. To answer the question of how long immunity persists and what effect this high-level immunity had on virus transmission, we performed a follow-up study in early November, 2020.

Methods

Of the 1259 adults that participated in the baseline study, 801 could be included in the follow-up. The study involved the analysis of binding and neutralizing antibodies and T cell responses. In addition, the incidence of SARS-CoV-2 infections in Ischgl was compared to the incidence in similar municipalities in Tyrol throughout 2020.

Findings

For the 801 individuals that participated in both studies, the seroprevalence declined from 51.4% (95% confidence interval (CI) 47.9 - 54.9) to 45.4% (95% CI 42.0 - 49.0). Median antibody concentrations dropped considerably but antibody avidity increased. T cell responses were analysed in 93 cases, including all 4 formerly seropositive cases that had lost antibodies in all assays, three of which still had detectable T cell memory. In addition, the incidence in the second COVID-19 wave that hit Austria in November 2020, was significantly lower in Ischgl than in comparable municipalities in Tyrol or the rest of Austria.

Interpretation

This study has important implications as it shows that although antibodies to SARS-CoV-2 declined, T and B cell memory can be detected for up to 8 months. Complemented by infection prevention measures a level of around 40-45% immunity in Ischgl significantly reduced local virus transmission during the second wave in Austria in November 2020.

Funding

Funding was provided by the government of Tyrol and the FWF Austrian Science Fund.

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