Objective To examine time-dependent variations in serum antibodies of severe acute respiratory disease coronavirus 2 (SARS-CoV-2) among confirmed coronavirus disease 2019 (COVID-19) cases at different stages and inactivated COVID-19 vaccine recipients after inoculation.
Methods The study was conducted in a city of Henan province. Totally 86 serum samples were collected from 43 confirmed COVID-19 cases at acute stage (1th – 23rd day of onset) and recovery state (25th – 58th day of onset) during January 2020 – October 2021; other 184 serum samples from 46 healthy recipients of inactivated COVID-19 vaccine at 4/8/12/31 weeks after inoculations and 50 serum samples from 50 residents without confirmed SARS-CoV-2 infections were also collected during March – October 2021. Anti-SARS-CoV-2 immunoglobulin A/G/M (IgA/G/M) were detected with magnetic particle chemiluminescence method and enzyme-linked immunosorbent assay for all the serum samples. The levels of the serum antibodies among the three groups′ participants were analyzed statistically.
Results Among the confirmed COVID-19 cases, the positivity rates of anti-SARS-CoV-2 IgA, IgM and IgG of the serum samples collected at recovery stage were significantly higher than those at acute stage (all P < 0.05) ; while, the concentrations of anti-SARS-CoV-2 IgM and IgG of the serum samples collected at recovery stage were significantly higher than those at acute stage (both P < 0.05). Among the healthy COVID-19 vaccine recipients 31 weeks after the inoculations, the positivity rate was 63.04% (29/46) for anti-SARS-CoV-2 IgG and 36.96% (17/46) for anti-SARS-CoV-2 IgA, but all samples were negative for anti-SARS-CoV-2 IgM. No significant differences were observed in the absorbance ratios anti-SARS-CoV-2 IgA among the samples collected 4, 8, 12, and 31weeks after the inoculation (F = 2.365, P = 0.073), but there were significant differences in the concentrations of anti-SARS-CoV-2 IgM and IgG (both P < 0.05) among the samples. Both the positivity rate of anti-SARS-CoV-2 IgA and IgM and the concentrations of anti-SARS-CoV-2 IgG and IgM were significantly higher among the confirmed COVID-19 cases than those among the inactivated COVID-19 vaccine recipients during a comparable period of time (P < 0.05 for all).
Conclusion The positivity rate of serum anti-SARS-CoV-2 IgG is the highest during early stage and recovery stage among COVID-19 cases. The positivity of serum anti-SARS-CoV-2 IgA and IgG occur earlier than that of IgM and could maintain till 31 weeks after the inoculation among inactivated COVID-19 vaccine recipients. The concentration of serum anti-SARS-CoV-2 IgG and IgM are higher among COVID-19 cases than those among inactivated COVID-19 vaccine recipients during a comparable period of time.
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