Changes of antibodies in COVID‑19 patients: A 10‑month prospective study

Objective: To explore the law of antibody changes in patients diagnosed with COVID‑19 after the onset of the disease. Methods: A total of 215 patients who were diagnosed with COVID‑19 by RT‑PCR in Wuchang District, Wuhan City, Hubei Province were recruited as the research subjects. The rapid colloidal gold immunochromatography assay was performed on every newly diagnosed patient at the time points of (10±3) d, (100±3) d, (190±3) d, and (280±3) d after the onset of the disease. Results: In terms of antibody types, among the 215 patients,the positive rate of IgM antibodies was 36.7% at (10±3) d. The antibody levels were 22.5%, 5.0%, and 4.7% at (100±3) d, (190±3) d, and (280±3) d respectively. In general, the levels of IgG antibody were high. The positive rate of antibody within (10±3) days was 87.0%, and the rate decreased to 80.8% at (100±3) d, 49.7% and 46.5% at (190±3) d and (280±3) d, respectively. The number of IgM and IgG antibodies homo‑positive samples gradually decreased over time. At the meantime, the proportion of IgM+IgG antibodies both negative samples gradually increases. According to the clinical classification, in the early stage of the disease, the positive rate of IgM antibody was different in patients with different severity of clinical symptoms. The more severe the clinical symptoms, the higher the positive rate of IgM antibodies. Around 190 days after the onset of symptoms, the positive rate of IgG antibodies decreased more slowly in mild and common patients. At the 280‑day during follow‑up, IgM antibodies showed a higher positive rate in severe and critical patients. From the trend of antibody changes in the same patient within 10 months, among the 70 patients, only 55 cases (32.4%) showed continuous positive in IgG antibody, with 77 cases (45.3%) in the IgG antibody positive‑to‑negative group,and 21 cases (12.4%) in the IgG antibody positive‑to‑negative‑to‑positive group. Three cases (1.8%) showed IgG antibody negative converting to positive. However, there were 14 cases (8.2%) remaining with negative IgG antibody. For IgM antibodies, 97 cases (57.1%) were persistently negative, wth 5 cases (2.9%) in the negative‑to‑positive group, and 65 cases (38.2%) in the positive‑to‑negative group. IgM antibody continued to be positive within 10 months has not been observed yet, and there were 3 cases (1.8%) in the IgM antibody positive‑to‑negative‑to‑positive group. Conclusion: After the new coronavirus infection, the serological response is unstable. In the early stage of the disease, antibody detection has important auxiliary value for the diagnosis of the disease;but in the late stage, the diagnostic value is not great. The antibody response may be positively correlated with the severity of the disease. Nearly 50% of patients can remain positive for IgG antibodies within 10 months, which indicates that nearly half of patients recovering from COVID‑19 can obtain longer‑lasting immunity. However, IgG antibodies in some patients continue or eventually become negative. Whether such patients can get immunity remains to be observed and studied. © 2021, Editorial Board of Medical Journal of Wuhan University. All right reserved.