27 Pages Posted: 10 Oct 2020More...
Studies on serologic responses following COVID-19 have been published primarily in individuals who are moderately or severely symptomatic, but there are few data from individuals who are only mildly symptomatic or asymptomatic. To generate such data, we used World Health Organization disease severity categorization, and measured IgG, IgM, and IgA antibodies to the receptor binding domain (RBD) of spike protein of SARS-CoV-2 by ELISA in infected individuals, both mildly symptomatic (n=108) and asymptomatic (n=63) on days 1, 7, 14, and 30 following RT-PCR-based confirmation of infection in Bangladesh, and compared these results to those detected in pre-pandemic samples, including healthy controls (n=73) and individuals infected with other viruses commonly seen in this area (n = 79). Mildly symptomatic individuals developed IgM and IgA antibody responses by day 14 after detection of infection in 72% and 83% of individuals, respectively, while 95% of these individuals developed an IgG antibody response by day 14, 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 by day 14, 22% positive for IgM by day 14, and 45% positive for IgG by day 30 after detection of infection. These results confirm that immune responses are generated following COVID in individuals who develop mildly symptomatic illness. However, those with asymptomatic infection do not respond or have lower antibody levels. These results will impact modelling needed for determining herd immunity generated by natural infection or vaccination.
Funding Statement: World Health Organization, Fogarty International Center TW005572 and Emerging Global Leader Award; K43 TW010362, the Fondation Merieux and the Bill and Melinda Gates Foundation (BMGF). This study was carried out with the support of the United States Agency for International Development (USAID) under the terms of USAID’s Alliance for Combating TB in Bangladesh activity cooperative agreement no. CA # 72038820CA00002.
Declaration of Interests: The authors declare no conflict of interest.
Ethics Approval Statement: The study was also approved by the IRB of the IEDCR and icddr,b.
Keywords: Seroconversion, COVID-19, immune responses, symptomatic, asymptomatic
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