Evaluation of humoral immune responses, effective factors on responses and re-infection in recovered COVID-19 patients

Introduction: Despite large studies on the COVID-19 pandemic, little evidence is available on immune response in recovered patients. Objectives: The aim of this study was to investigate the humoral immune responses (IgM and IgG antibodies) in recovered COVID-19 patients and the role of risk factors and symptoms with respect to the immune responses. Patients and Methods: In this descriptive-analytical study, which was conducted by call-out method, the serum levels of IgM and IgG antibodies were measured using enzyme-linked immunosorbent assay (ELISA) in 248 recovered patients. Effective factors on immune response were determined. Re-infection was investigated through patient follow-up and using information drawn from the hospital information system. Chi-square, t test, ANOVA, and regression analysis in SPSS 15 and Stata 14 were conducted to investigate the relationship between variables. Results: IgG positivity was 86.3% among our participants. Among those who did not show antibody response to COVID-19 (IgM- and IgG-), the most common symptoms at admission were fever, muscle pain (90.9%), chills and anorexia (81.8%). IgG levels remained positive in recovered patients for over seven months. IgG response showed a significant relationship with body mass index, hospital stay length, smoking, residence place, mortality rate, vomiting, and appetite (P<0.05). The re-infection rate after recovery was only 1.6%. Conclusion: High seroprevalence of IgG antibody against COVID-19 and low re-infection rate in Chaharmahal and Bakhtiari province was observed. In addition, the effects of factors such as fever, muscle pain, chills, vomiting, and anorexia on immune responses were demonstrated. These results can be used to manage disease control efficiently, and follow up the treatment process and re-infection in the recovered patients.