Estimation of real COVID-19 cases in India during the first wave

In 2020, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) spread across the world within a few months. The SARS-CoV-2 pandemic has had a devastating effect on humanity, with social and economic consequences. The continents of Europe and America have been hit the hardest. However, there has also been a huge loss of life in India, with the country having the fourth highest number of total deaths worldwide. Nevertheless, the infection and death rates per million and the case fatality ratio in India are substantially lower than those in many developed nations. Several explanations for this have been proposed, including genetics. Mathematical modelling has suggested that the actual number of infections is much higher than the number of reported cases. Therefore, to understand the dynamics of actual infection and the population-level immunity against SARS-CoV-2, a serosurvey (antibody testing) was performed among 2301 individuals in urban regions of 14 districts in six states of India. A notable outcome of this study was that a large proportion of the Indian population had an asymptomatic SARS-CoV-2 infection. The real infection rate in India was several fold higher than the reported number of cases. Therefore, a large number of people in the country have developed SARS-CoV-2-specific antibodies. In this survey, the seroprevalence (frequency antibody-positive) varied between 0.01 (95% CI 0.002-0.054) and 0.477 (95% CI 0.392-0.563), suggesting a high variability in viral transmission between the states and the possibility of future waves. In this study population, the frequency of asymptomatic infection was highest in the younger age groups. It was also found that the numbers of cases reported by the government were several-fold lower than the real incidence of infection. It is likely that the high number of asymptomatic cases was the main driver of this discrepancy.