The Status of Antibody Production and its Stability after Infection in Outpatients with Covid-19

Covid-19 is a viral disease of the respiratory system. Considering that the persistence of antibodies against COVID-19 has been different in the reports and since ethnic and racial differences have been effective in this status, the purpose of this study was to examine the status of antibodies and persistence in patients with COVID-19.

This longitudinal study was conducted in 2019 on patients referred to a fever clinic in Miandorod City. The diagnosis of the disease was based on the history and real-time PCR test or lung CT scan. 87 patients were included in the study based on the diagnostic criteria, and the exclusion criteria included cases of non-return in the follow-up. The level of IgM and IgG antibodies was measured by ELISA method and Pishtaz Teb kit at the beginning of the diagnosis, and to check the stability, the IgG level of the same patients was rechecked 6 months later, and according to the instructions of the kit, values higher than 1.1 were considered positive. Data including background information, lung involvement in CT scan, and ELISA results were analyzed after entering the computer with SPSS 21 statistical software and T-test and Fisher's exact tests. P<0.05 was considered a significance level.

The mean age of the patients was 47.7±17 years. 55 people (63%) were women, 20 people (23%) had high blood pressure and 18 people (20.7%) had diabetes. 84 patients had positive real-time PCR tests, and 43 patients (49.4%) had CT lung involvement. Initial IgM was positive in 20 people (23%), initial IgG was positive in 58 people (66.7%), and after six months IgG was positive in 36 cases (41.4%). Antibody was stable in 67.4% of men and 56.4% of women (P=0.41). High blood pressure (P=0.329) diabetes (P=0.21) and lung involvement in CT scan (P=0.586) had no significant relationship with antibody stability. The average age of people with stable antibodies (50 ± 16.2 years) and those whose antibody was negative (42±14.1 years) had no significant difference (P=0.077).

The findings showed that the antibody against the disease was not produced in one-third of the patients and after 6 months, the amount of IgG had decreased in a significant part of the patients. Also, the results showed that antibody stability had no significant relationship with age, gender, lung involvement in CT scans, and underlying diseases such as hypertension and diabetes.