We categorised the reported occupations into high-risk and low-risk categories, on the basis of the potential risk of exposure to a known or unknown COVID-19 case. We described the characteristics of study participants as percentages, means, and SDs. We also found evidence of seroconversion among those without symptoms or known exposure, highlighting the limitations of symptom-directed or exposure-directed testing. Our findings indicate a substantial transmission in rural areas, although seroprevalence continues to be higher in urban slum and non-slum areas. We found no difference in seropositivity by age group, sex, or occupation. We estimated that for every reported case of COVID-19 there were 26–32 infections, and the infection-fatality ratio in surveyed districts was 0♰9–0♱1%. Our findings indicate an overall seroprevalence of around 7% among individuals aged 10 years or older, with a tenfold increase in adult seroprevalence between May and August, 2020. This population-based study represents seroprevalence at the national level, covering many areas across India's large expanse. Furthermore, Indian cities represent challenging conditions for COVID-19 control, with some of the world's highest population densities and contact rates. Because of India's large size, geographical diversity, and population heterogeneity, it is difficult to understand the extent of transmission of SARS-CoV-2 using case-based surveillance data alone. India represents one of the largest populations at risk of COVID-19 and as of Sept 30, 2020, had reported the second highest number of confirmed cases globally. The first national SARS-CoV-2 serosurvey in India indicated an overall low seroprevalence among adults by May, 2020, and the majority of infections were in people living in urban areas, with an estimated 82–130 infections for every reported COVID-19 case. Most studies were limited to smaller subnational areas, few were representative of the population as a whole, and potential sources of bias included the method of participant selection, non-response rates, and misclassification resulting from test specificity, particularly when the prevalence was low.
Several studies describing the seroprevalence of SARS-CoV-2 had been done across various geographical areas, using different sampling and recruitment strategies, as well as a range of testing approaches. We reviewed the evidence for the seroprevalence of SARS-CoV-2 available as of Sept 30, 2020, by searching the National Library of Medicine article database and medRxiv for preprint publications, published in English, using the terms “serology”, “seroconversion”, “serosurveillance”, “seroepidemiology”, “seroprevalence”, “seropositivity”, “SARS-CoV-2”, and “COVID-19”. The seroprevalence of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) antibodies is important to understand the transmission dynamics of the virus estimate total infections, including mild and asymptomatic individuals who might not receive testing and inform the possibility of transmission interruption through the depletion of susceptible individuals, if seroconversion is associated with robust immunity.
The Lancet Regional Health – Western Pacific.The Lancet Regional Health – Southeast Asia.The Lancet Gastroenterology & Hepatology.
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