SARS-CoV-2 antibody dynamics over time and risk factors associated with infection and long COVID-19 symptoms in large working environments

J Intern Med. 2023 Jun;293(6):763-781. doi: 10.1111/joim.13637. Epub 2023 Apr 17.


Background: Factors influencing SARS-CoV-2 antibody dynamics, transmission, waning and long COVID-19 symptomatology are still not fully understood.

Methods: In the Danish section of the Novo Nordisk Group, we performed a prospective seroepidemiological study during the first and second waves of the COVID-19 pandemic. All employees and their household members (>18 years) were invited to participate in a baseline (June-August 2020), 6-month follow-up (December 2020-January 2021), and 12-month follow-up (August 2021) sampling. In total, 18,614 accepted and provided at least one blood sample and completed a questionnaire regarding socioeconomic background, health status, previous SARS-CoV-2 infection, and persistent symptoms. Total antibody and specific IgM, IgG and IgA levels against recombinant receptor binding domain were tested.

Results: At baseline, the SARS-CoV-2-antibody seroprevalence was 3.9%. At 6-month follow-up, the seroprevalence was 9.1%, while at 12-month follow-up, the seroprevalence was 94.4% (after the vaccine roll-out). Male sex and younger age (18-40 years) were significant risk factors for seropositivity. From baseline to the 6-month sampling, we observed a substantial waning of IgM, IgG and IgA levels (p < 0.001), regardless of age, sex and initial antibody level. An increased antibody level was found in individuals infected prior to vaccination compared to vaccinated infection naïves (p < 0.0001). Approximately a third of the seropositive individuals reported one or more persistent COVID-19 symptoms, with anosmia and/or ageusia (17.5%) and fatigue (15.3%) being the most prevalent.

Conclusion: The study provides a comprehensive insight into SARS-CoV-2 antibody seroprevalence following infection and vaccination, waning, persistent COVID-19 symptomatology and risk factors for seropositivity in large working environments.

Keywords: SARS-CoV-2; antibody; infection; long COVID; transmission; waning; working environment.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adolescent
  • Adult
  • Antibodies, Viral
  • COVID-19* / epidemiology
  • Humans
  • Immunoglobulin A
  • Immunoglobulin G
  • Immunoglobulin M
  • Male
  • Pandemics
  • Post-Acute COVID-19 Syndrome
  • Prospective Studies
  • Risk Factors
  • SARS-CoV-2
  • Seroepidemiologic Studies
  • Working Conditions
  • Young Adult


  • Antibodies, Viral
  • Immunoglobulin A
  • Immunoglobulin G
  • Immunoglobulin M