SARS-CoV-2-directed antibodies persist for more than six months in a cohort with mild to moderate COVID-19

Infection. 2021 Aug;49(4):739-746. doi: 10.1007/s15010-021-01598-6. Epub 2021 Mar 10.


Objective: To follow serological immune responses of front-line healthcare workers after PCR-confirmed COVID-19 for a mean of 30 weeks, describe the time-course of SARS-CoV-2 spike protein-specific IgG, IgA and IgM levels and to identify associations of the immune response with symptoms, demographic parameters and severity of disease.

Methods: Anti-SARS-CoV-2 S protein-specific IgG, IgA and IgM antibodies were measured at three time points during the 30-week follow-up. COVID-19-specific symptoms were assessed with standardized questionnaires.

Results: 95% of the participants mounted an IgG response with only modest decline after week 12. IgG-type antibodies were still detectable in almost 90% of the subjects at 30 weeks. IgA and IgM responses were less robust and antibody titers decreased more rapidly. At 30 weeks, only 25% still had detectable IgA-type and none had IgM-type antibodies. Higher age and higher disease severity were independently associated with higher IgG antibody levels, albeit with wide variations.

Conclusion: Serological immune responses after COVID-19 show considerable inter-individual variability, but show an association with increasing age and higher severity of disease. IgG-type anti-SARS-CoV-2 antibodies remain positive in 90% of the individuals 30 weeks after onset of symptoms.

Keywords: Antibody titer; COVID-19; ELISA; SARS-CoV-2; Serological immune response; Severity of disease.

MeSH terms

  • Adolescent
  • Adult
  • Algorithms
  • Antibodies, Viral / blood*
  • COVID-19 / immunology*
  • Cohort Studies
  • Enzyme-Linked Immunosorbent Assay
  • Female
  • Humans
  • Immunoglobulin A / blood
  • Immunoglobulin G / blood
  • Immunoglobulin M / blood
  • Male
  • Middle Aged
  • SARS-CoV-2 / immunology*
  • Severity of Illness Index
  • Surveys and Questionnaires
  • Time Factors
  • Young Adult


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