Seroprevalence and Dynamics of anti-SARS-CoV-2 antibody among healthcare workers following ChAdOx1 nCoV-19 vaccination

Abstract Background The serological evaluations of IgG, IgM, and IgA to the SARS-CoV-2 proteins are widely used for the epidemiological assessment of COVID-19. The Health Care Workers (HCWs) are presumably exposed to a higher risk of acquiring the disease owing to their regular contact with the patients. Methods COVID-19 prevalence was investigated by classifying 313 HCWs into four groups based on their degree of exposure and estimating the IgG and total antibody. The serological assessment of the anti-SARS-CoV-2 antibody was conducted 21 days post-vaccination of first or both doses of the ChAdOx1 nCoV-19 vaccine among 174 HCWs. The vaccinated HCWs were followed up for 3 months for SARS-CoV-2 infection. Findings The levels of anti-SARS-CoV-2 IgG were comparable among different groups, but the seroprevalence gradually decreased from the most exposed to the less exposed group. The neutralizing antibody was positively correlated with IgG as well as total antibody. IgG was marginally decreased after 2 months followed by a significant drop after 4-6 months post-infection. However, 80% of the HCWs developed a detectable amount of IgG after the first dose of vaccination, the median titer of which was comparable to the seropositive HCWs after natural infection. Almost 100% of the HCWs developed antibodies after the second dose of vaccine with boosting effect among the seropositive HCWs. Although ∼11.5% of the vaccinated HCWs were infected with the SARS-CoV-2, ∼94% of them showed mild symptoms and recovered in home isolation without any O2 support. Interpretations The varying level of seroprevalence among the four groups suggested stratified spread of the disease. One dose of SARS-CoV-2 vaccination was found to be effective in terms of the antibody titer, while the second dose was required to cover the larger population. The effectiveness of the ChAdOx1 nCoV-19 vaccine was noticeable due to the low rate of post-vaccination infection with moderate or severe symptoms.