SARS-CoV-2 IgG antibody responses in rt-PCR-positive cases: first report from India

INTRODUCTION: Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) antibody responses remain poorly understood and the clinical utility of serological testing is still unclear. AIM: To understand the relationship between the antibody response to SARS-CoV-2 infection and the demographics and cycle threshold (C (t)) values of confirmed RT-PCR patients. METHODOLOGY: A total of 384 serum samples were collected from individuals between 4–6 weeks after confirmed SARS-CoV-2 infection and tested for the development of immunoglobulin class G (IgG) against SARS-CoV-2. The C (t) values, age, gender and symptoms of the patients were correlated with the development of antibodies. RESULTS: IgG positivity was found to be 80.2 % (95 % CI, 76.2–84.2). Positivity increased with a decrease in the C (t) value, with the highest (87.6 %) positivity observed in individuals with C (t) values <20. The mean (±sd) C (t) values for IgG positives and negatives were 23.34 (±6.09) and 26.72 (±7.031), respectively. No significant difference was found for demographic characteristics such as age and sex and symptoms and antibody response. The current study is the first of its kind wherein we have assessed the correlation of the RT-PCR C (t) with the development of IgG against SARS-CoV-2. CONCLUSION: Although C (t) values might not have any relation with the development of symptoms, they are associated with the antibody response among SARS-CoV-2-infected individuals.