Longitudinal serology in SARS-CoV-2 infected individuals in India – a prospective cohort study

Clinical and epidemiological characteristics of SARS-CoV-2 infection are now widely available, but there are few data on longitudinal serology in large cohorts, particularly from low-and middle-income countries. We established an ongoing prospective cohort of 3840 SARS-CoV-2 RT-PCR positive individuals in the Delhi-National Capital Region of India, to document clinical and immunological characteristics during illness and convalescence. The IgG responses to the receptor binding domain (RBD) and nucleocapsid were assessed at 0-7, 10-28 days and 6-10 weeks after infection. The clinical predictors of seroconversion were identified by multivariable regression analysis. The seroconversion rates in the post-infection windows of 0–7 days, 10–28 days and 6–10 weeks were 46%, 84.7% and 85.3% respectively (n=782). The proportion with a serological response increased with severity of COVID-19 disease. All participants with severe disease, 89.6% with mild to moderate infection and 77.3% of asymptomatic participants had IgG antibodies to the RBD antigen. The threshold values in the nasopharyngeal viral RNA RT-PCR in a subset of asymptomatic and symptomatic seroconverters were comparable (p value: 0.48), with similar results among non-seroconverters (p value: 0.16) (n=169). This is the first report of longitudinal humoral immune responses to SARS-CoV-2 infection over a period of ten weeks from South Asia. The low seropositivity in asymptomatic participants and differences between assays highlight the importance of contextualizing the understanding of population serosurveys.