Antibody responses after COVID-19 infection in patients who are mildly symptomatic or asymptomatic in Bangladesh

Int J Infect Dis. 2020 Dec;101:220-225. doi: 10.1016/j.ijid.2020.09.1484. Epub 2020 Oct 5.


Objectives: Studies on serological responses following coronavirus disease-2019 (COVID-19) have been published primarily in individuals who are moderately or severely symptomatic, but there are few data from individuals who are mildly symptomatic or asymptomatic.

Methods: We measured IgG, IgM, and IgA to the receptor-binding domain of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) by using enzyme-linked immunosorbent assay in mildly symptomatic (n = 108) and asymptomatic (n = 63) on days 1, 7, 14, and 30 following RT-PCR confirmation in Bangladesh and when compared with pre-pandemic samples, including healthy controls (n = 73) and individuals infected with other viruses (n = 79).

Results: Mildly symptomatic individuals developed IgM and IgA responses by day 14 in 72% and 83% of individuals, respectively, while 95% of individuals developed IgG response, and rose to 100% by day 30. In contrast, individuals infected with SARS-CoV-2 but who remained asymptomatic developed antibody responses significantly less frequently, with only 20% positive for IgA and 22% positive for IgM by day 14, and 45% positive for IgG by day 30 after infection.

Conclusions: These results confirm immune responses are generated following COVID-19 who develop mildly symptomatic illness. However, those with asymptomatic infection do not respond or have lower antibody levels. These results will impact modeling needed for determining herd immunity generated by natural infection or vaccination.

Keywords: Asymptomatic; COVID-19; Immune responses; Seroconversion; Symptomatic.

MeSH terms

  • Adult
  • Antibodies, Viral / blood
  • Antibodies, Viral / immunology*
  • Antibody Formation
  • Bangladesh / epidemiology
  • COVID-19 / blood
  • COVID-19 / epidemiology
  • COVID-19 / immunology*
  • COVID-19 / virology
  • Carrier State / blood
  • Carrier State / epidemiology
  • Carrier State / immunology*
  • Carrier State / virology
  • Enzyme-Linked Immunosorbent Assay
  • Female
  • Humans
  • Immunoglobulin G / blood
  • Immunoglobulin G / immunology
  • Immunoglobulin M / blood
  • Immunoglobulin M / immunology
  • Male
  • Middle Aged
  • Pandemics
  • SARS-CoV-2 / genetics
  • SARS-CoV-2 / immunology*


  • Antibodies, Viral
  • Immunoglobulin G
  • Immunoglobulin M