Cycle threshold values are associated with adaptive immunity to COVID-19– a case-control study in Qatar

Background We investigated the prevalence of detectable SARS-CoV-2 specific antibodies and its determinants, including the cycle threshold value of the polymerase chain reaction (Ct value), in a Middle Eastern cohort, where these data have not been previously reported. Methods In this longitudinal study of participants in Qatar who recovered from COVID-19, data on demographics, comorbidities, Ct values, and antibody titters were collected at baseline and antibody titres measured monthly thereafter. Multiple variable logistic regression was performed to explore determinants of humoral immunity, with the binary outcome of antibody reactivity one month after recovery. Results We included 225 participants with a median age of 42.2 (IQR 32.2–52.3) of which 53.8% were female and 38.7% were of Qatari nationality. At one month after recovery, 177 (78.7%) participants had anti-SARS-CoV-2 IgG antibodies. Male gender and a Ct value < 20 were associated with higher odds of anti-SARS-CoV-2 IgG antibodies (OR 3.24, 95% CI 1.53–6.89), (OR 2.03, 95% CI 0.97–4.24), respectively. Conclusion In a Middle Eastern setting, nearly 80% of individuals with confirmed COVID-19 showed reactive IgG antibodies at one month follow up. The male sex and a Ct Value < 20 were associated with higher odds of reactive IgG antibodies.