Background There are few studies on the long-term follow-up of virus-specific antibodies in COVID-19 survivors after discharge, and most results of the existing studies are influenced by vaccination. Therefore, elaborating the dynamic changes of virus-specific antibody levels in the natural infection state is of great practical value for predicting the antibody protective capacity, the risk of reinfection in COVID-19 patients and guiding vaccination.
Objective To describe the changes in virus-specific antibodies in COVID-19 survivors discharged from the hospital without vaccine interference through long-term and multiple follow-ups.
Methods We followed up with COVID-19 patients discharged from a hospital in Wuhan from February 15, 2020, to April 5, 2020, for 12 months. At three follow-up time points of 6, 9, and 12 months after discharge, the enrolled patients retained peripheral blood samples for detection of virus-specific antibodies for COVID-19.
Results Total IgM antibody levels in COVID-19 patients significantly declined at 6 months post-discharge and tested negative (<10 AU/mL). Total IgG antibody levels likewise dramatically declined at 6 months post-discharge, and they were relatively stable from 6 to 9 months, and significantly decreased from 9 to 12 months, but still tested positive at 12 months post-discharge (>10 AU/mL, 94.44%). Anti-nucleocapsid IgG antibody showed a persistent and considerable decline throughout the follow-up period and remained positive at 12 months post-discharge, with a positive rate of 96.08%. The levels of anti-spike protein IgG antibody, anti-receptor binding domain IgG antibody, and neutralizing antibody remained relatively stable from 6 months to 9 months after discharge, but significantly decreased from 9 months to 12 months, and were positive at 12 months after discharge. Age, gender, clinical classification, and underlying disease had no significant effect on antibody levels and their trends after discharge.
Conclusion The levels and decreasing trends of various types of specific antibodies after COVID-19 infection are different, with some antibodies remaining at high levels in COVID-19 survivors at 12 months after discharge. There are no significant differences in levels and decreasing trends of antibodies between ages, gender, clinical classification of COVID-19, and underlying disease.
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