Clin Microbiol Infect
. 2021 Sep 17;S1198-743X(21)00495-X.
doi: 10.1016/j.cmi.2021.09.005. Online ahead of print.
Seroprevalence of SARS-CoV-2 antibodies and reduced risk of reinfection through six months: a Danish observational cohort study of 44,000 healthcare workers
Kasper Iversen 1 , Jonas Henrik Kristensen 2 , Rasmus Bo Hasselbalch 2 , Mia Pries-Heje 3 , Pernille Brok Nielsen 2 , Andreas Dehlbæk Knudsen 4 , Kamille Fogh 2 , Jakob Boesgaard Norsk 2 , Ove Andersen 5 , Thea Køhler Fischer 6 , Claus Antonio Juul Jensen 7 , Christian Torp-Pedersen 6 , Jørgen Rungby 8 , Sisse Bolm Ditlev 9 , Ida Hageman 10 , Rasmus Møgelvang 3 , Mikkel Gybel-Brask 11 , Ram B Dessau 12 , Erik Sørensen 11 , Lene Harritshøj 11 , Fredrik Folke 13 , Curt Sten 14 , Maria Elizabeth Engel Møller 15 , Thomas Benfield 16 , Henrik Ullum 17 , Charlotte Sværke Jørgensen 17 , Christian Erikstrup 18 , Sisse R Ostrowski 11 , Susanne Dam Nielsen 19 , Henning Bundgaard 20
Affiliations
- PMID: 34543759
- DOI: 10.1016/j.cmi.2021.09.005
Abstract
Objectives: Antibodies to severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) are a key factor against COVID-19. We examined longitudinal changes in seroprevalence in healthcare workers (HCW) 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 HCW three times over six months. HCW-characteristics were obtained by questionnaires. ClinicalTrials.gov, NCT04346186.
Results: From April to October 2020 we screened 44,698 HCW of which 2,811 were seropositive at least once. The seroprevalence increased from 4.0% (1,501/37,452) to 7.4% (2,022/27,457) during the period (p<0.001) and was significantly higher than in non-HCW. Frontline HCW had a significantly increased risk of seropositivity compared to non-frontline HCW with risk ratios (RR) 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 HCW from dedicated COVID-19 wards compared to other frontline HCW. Seropositive HCW had a RR of 0.35 (0.15-0.85, p=0.012) of reinfection during the following six months and 2,115 (95%) out of 2,248 of those who were seropositive during rounds one or two remained seropositive after four to six months. The 133 of 2,248 (5.0%) participants who seroreverted were slightly older and reported fewer symptoms than other seropositive participants.
Conclusions: HCW remained at increased risk of infection with SARS-CoV-2 during the six months period. Seropositivity against SARS-CoV-2 persisted for at least six months in the vast majority of HCW and was associated with a significantly lower risk of reinfection.