SARS-CoV-2 Seroprevalence and Antibody Kinetics Among Health Care Workers in a Spanish Hospital After 3 Months of Follow-up

J Infect Dis. 2021 Jan 4;223(1):62-71. doi: 10.1093/infdis/jiaa696.


Background: At the COVID-19 spring 2020 pandemic peak in Spain, prevalence of SARS-CoV-2 infection in a cohort of 578 randomly selected health care workers (HCWs) from Hospital Clínic de Barcelona was 11.2%.

Methods: A follow-up survey 1 month later (April-May 2020) measured infection by rRT-PCR and IgM, IgA, and IgG to the receptor-binding domain of the spike protein by Luminex. Antibody kinetics, including IgG subclasses, was assessed until month 3.

Results: At month 1, the prevalence of infection measured by rRT-PCR and serology was 14.9% (84/565) and seroprevalence 14.5% (82/565). We found 25 (5%) new infections in 501 participants without previous evidence of infection. IgM, IgG, and IgA levels declined in 3 months (antibody decay rates 0.15 [95% CI, .11-.19], 0.66 [95% CI, .54-.82], and 0.12 [95% CI, .09-.16], respectively), and 68.33% of HCWs had seroreverted for IgM, 3.08% for IgG, and 24.29% for IgA. The most frequent subclass responses were IgG1 (highest levels) and IgG2, followed by IgG3, and only IgA1 but no IgA2 was detected.

Conclusions: Continuous and improved surveillance of SARS-CoV-2 infections in HCWs remains critical, particularly in high-risk groups. The observed fast decay of IgA and IgM levels has implications for seroprevalence studies using these isotypes.

Keywords: COVID-19; SARS-CoV-2; antibodies; health care workers; kinetics; longitudinal cohort; seroprevalence.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Antibodies, Viral / blood*
  • COVID-19 / immunology*
  • Cross-Sectional Studies
  • Female
  • Follow-Up Studies
  • Health Personnel*
  • Humans
  • Immunoglobulin A / blood
  • Immunoglobulin G / blood
  • Immunoglobulin M / blood
  • Kinetics
  • Male
  • Middle Aged
  • Seroconversion
  • Seroepidemiologic Studies
  • Spain / epidemiology


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