Susanne Nielsen

Seroprevalence of SARS-CoV-2 antibodies and reduced risk of reinfection through 6 months: a Danish observational cohort study of 44 000 healthcare workers

Research output: Contribution to journal/Conference contribution in journal/Contribution to newspaperJournal articleResearchpeer-review

  • Kasper Iversen, University of Copenhagen
  • ,
  • Jonas Henrik Kristensen, University of Copenhagen
  • ,
  • Rasmus Bo Hasselbalch, University of Copenhagen
  • ,
  • Mia Pries-Heje, University of Copenhagen
  • ,
  • Pernille Brok Nielsen, University of Copenhagen
  • ,
  • Andreas Dehlbæk Knudsen, University of Copenhagen
  • ,
  • Kamille Fogh, University of Copenhagen
  • ,
  • Jakob Boesgaard Norsk, University of Copenhagen
  • ,
  • Ove Andersen, University of Copenhagen
  • ,
  • Thea Køhler Fischer, University of Copenhagen
  • ,
  • Claus Antonio Juul Jensen, University of Copenhagen
  • ,
  • Christian Torp-Pedersen, University of Copenhagen
  • ,
  • Jørgen Rungby
  • Sisse Bolm Ditlev, University of Copenhagen
  • ,
  • Ida Hageman, University of Copenhagen, Capitol Region of Denmark
  • ,
  • Rasmus Møgelvang, University of Copenhagen
  • ,
  • Mikkel Gybel-Brask, University of Copenhagen
  • ,
  • Ram B. Dessau, Sjællands Universitetshospital, University of Southern Denmark
  • ,
  • Erik Sørensen, University of Copenhagen
  • ,
  • Lene Harritshøj, University of Copenhagen
  • ,
  • Fredrik Folke, University of Copenhagen
  • ,
  • Curt Sten, University of Copenhagen
  • ,
  • Maria Elizabeth Engel Møller, University of Copenhagen
  • ,
  • Thomas Benfield, University of Copenhagen
  • ,
  • Henrik Ullum, Statens Serum Institut
  • ,
  • Charlotte Sværke Jørgensen, Statens Serum Institut
  • ,
  • Christian Erikstrup
  • Sisse R. Ostrowski, University of Copenhagen
  • ,
  • Susanne Dam Nielsen
  • Henning Bundgaard, University of Copenhagen

Objectives: Antibodies to severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) are a key factor in protecting against coronavirus disease 2019 (COVID-19). We examined longitudinal changes in seroprevalence in healthcare workers (HCWs) in Copenhagen and the protective effect of antibodies against SARS-CoV-2. Methods: In this prospective study, screening for antibodies against SARS-CoV-2 (ELISA) was offered to HCWs three times over 6 months. HCW characteristics were obtained by questionnaires. The study was registered at ClinicalTrials.gov, NCT04346186. Results: From April to October 2020 we screened 44 698 HCWs, of whom 2811 were seropositive at least once. The seroprevalence increased from 4.0% (1501/37 452) to 7.4% (2022/27 457) during the period (p < 0.001) and was significantly higher than in non-HCWs. Frontline HCWs had a significantly increased risk of seropositivity compared to non-frontline HCWs, with risk ratios (RRs) at the three rounds of 1.49 (95%CI 1.34–1.65, p < 0.001), 1.52 (1.39–1.68, p < 0.001) and 1.50 (1.38–1.64, p < 0.001). The seroprevalence was 1.42- to 2.25-fold higher (p < 0.001) in HCWs from dedicated COVID-19 wards than in other frontline HCWs. Seropositive HCWs had an RR of 0.35 (0.15–0.85, p 0.012) of reinfection during the following 6 months, and 2115 out of 2248 (95%) of those who were seropositive during rounds one or two remained seropositive after 4–6 months. The 133 of 2248 participants (5.0%) who seroreverted were slightly older and reported fewer symptoms than other seropositive participants. Conclusions: HCWs remained at increased risk of infection with SARS-CoV-2 during the 6-month period. Seropositivity against SARS-CoV-2 persisted for at least 6 months in the vast majority of HCWs and was associated with a significantly lower risk of reinfection.

Original languageEnglish
JournalClinical Microbiology and Infection
Volume28
Issue5
Pages (from-to)710-717
Number of pages8
ISSN1198-743X
DOIs
Publication statusPublished - May 2022

    Research areas

  • COVID, Healthcare workers, Immune response, SARS-CoV-2, Seroprevalence

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