Investigation of Factors Affecting IgG Antibody Response in COVID-19 Cases

Objective: His study aimed to evaluate the factors influencing antibody titers and duration of antibody positivity against SARS-CoV-2 in COVID-19 patients followed for a year. Methods: Adult patients diagnosed with COVID-19 between March and August 2020 were included. Patient data, including age, gender, body mass index (BMI), Charlson comorbidity index (CCI), and clinical severity scores, were recorded. Patients were evaluated four times, and quantitative antibody titers were measured. Results: 53.1% of 177 patients were male, with a median age of 47 (IQR=33.5-55). 39.5% had additional comorbidities. Based on clinical severity, 33.3% were mild, 46.9% were moderate, and 19.8% were severe cases. The median intervals at visits were 56. 92, 193, and 371 days. Antibody positivity rates decreased, with 88.7%, 80.8%, 45.9%, and 21.4% at each visit. Median SARS-CoV-2 anti-N IgG titers decreased, particularly at the third visit (p<0.0001). Significant correlations were found between anti-N IgG titers and disease severity. Multivariate analysis showed that as disease severity increased, the probability of antibody positivity at the first and third visits increased approximately 3 to 6 times. Age and CCI score were also independent variables affecting antibody positivity. Conclusion: We observed a significant decrease in anti-N IgG antibody titers, especially after six months, and a considerable decline within one year. Disease severity was the most significant factor affecting antibody positivity, followed by age and CCI score. The study suggests further research to understand the duration of SARS-CoV-2-induced antibodies, seropositivity, and protective immunity.