Robust humoral and cellular immune responses and low risk for reinfection at least 8 months following asymptomatic to mild COVID-19

J Intern Med. 2022 Jan;291(1):72-80. doi: 10.1111/joim.13387. Epub 2021 Sep 27.


Background: Emerging data support detectable immune responses for months after severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection and vaccination, but it is not yet established to what degree and for how long protection against reinfection lasts.

Methods: We investigated SARS-CoV-2-specific humoral and cellular immune responses more than 8 months post-asymptomatic, mild and severe infection in a cohort of 1884 healthcare workers (HCW) and 51 hospitalized COVID-19 patients. Possible protection against SARS-CoV-2 reinfection was analyzed by a weekly 3-month polymerase chain reaction (PCR) screening of 252 HCW that had seroconverted 7 months prior to start of screening and 48 HCW that had remained seronegative at multiple time points.

Results: All COVID-19 patients and 96% (355/370) of HCW who were anti-spike IgG positive at inclusion remained anti-spike IgG positive at the 8-month follow-up. Circulating SARS-CoV-2-specific memory T cell responses were detected in 88% (45/51) of COVID-19 patients and in 63% (233/370) of seropositive HCW. The cumulative incidence of PCR-confirmed SARS-CoV-2 infection was 1% (3/252) among anti-spike IgG positive HCW (0.13 cases per 100 weeks at risk) compared to 23% (11/48) among anti-spike IgG negative HCW (2.78 cases per 100 weeks at risk), resulting in a protective effect of 95.2% (95% CI 81.9%-99.1%).

Conclusions: The vast majority of anti-spike IgG positive individuals remain anti-spike IgG positive for at least 8 months regardless of initial COVID-19 disease severity. The presence of anti-spike IgG antibodies is associated with a substantially reduced risk of reinfection up to 9 months following asymptomatic to mild COVID-19.

Keywords: COVID-19; SARS-CoV-2; humoral response; long-term immunity; reinfection.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Antibodies, Viral / blood*
  • Antibodies, Viral / immunology
  • Asymptomatic Infections
  • COVID-19 / diagnosis*
  • COVID-19 / immunology*
  • COVID-19 Nucleic Acid Testing
  • COVID-19 Serological Testing
  • Female
  • Humans
  • Immunity, Cellular*
  • Immunity, Humoral*
  • Immunoglobulin G / blood
  • Immunoglobulin G / immunology*
  • Male
  • Memory T Cells
  • Middle Aged
  • Pandemics
  • Reinfection*
  • SARS-CoV-2
  • Time Factors


  • Antibodies, Viral
  • Immunoglobulin G