Evaluation of Serum Antibody Levels and Presence of Neutralizing Antibodies in Mild and Moderate COVID-19 Patients

Introduction: Severe acute respiratory syndrome-Coronavirus-2 (SARS-CoV-2) antibodies are produced in persons who have been infected by the virus or have received the vaccine. Many features of these antibodies, including their dynamics and neutralization capacities, are still unclear. Understanding the immune response of the host is very important for the development of appropriate treatment methods, vaccines, and epidemiological control strategies. The present study aimed to monitor the change in antibody levels over time in individuals diagnosed with SARSCoV- 2 infections and to determine their neutralization capacity. Material(s) and Method(s): Anti-nucleocapsid and anti-spike antibody titers were measured using different kits on monthly obtained serum samples of patients of patients with SARS-CoV-2 infection. The neutralizing antibodies were evaluated using a microneutralization assay. Result(s): A total of 134 serum samples taken from 43 patients with a mild-moderate disease course were analyzed. Anti-spike antibody positivity was detected on day seven at the earliest and day 334 at the latest following a positive polymerase chain reaction (PCR) test. The mean antibody levels were observed to increase gradually to a peak after three months, and then started to decrease after month six. Anti-nucleocapsid IgM and IgG antibodies were detected alone or in combination. The highest neutralizing antibody titer was 1/80 in the first month, which was seen to drop below 1/10 after four months. Conclusion(s): The combined use of kits for the detection of antibodies against different antigens or testing total antibodies would result in a more accurate and earlier detection of the antibodies that start to emerge on the seventh day and decrease six months after SARS-CoV-2 PCR positivity. In addition, the dramatic decrease in neutralizing antibody titers after four months may be one of the causes of early reinfections. Copyright © 2022 by the Infectious Diseases and Clinical Microbiology Specialty Society of Turkey.