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Hvidovre Hospital - en del af Københavns Universitetshospital

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

Publikation: Bidrag til tidsskriftTidsskriftartikelForskningpeer review


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

TidsskriftClinical microbiology and infection : the official publication of the European Society of Clinical Microbiology and Infectious Diseases
Udgave nummer5
Sider (fra-til)710-717
Antal sider8
StatusUdgivet - maj 2022

ID: 67655661