Approximately one in 15 individuals aged 10 years or older in India is likely to have gone through a SARS-CoV-2 infection by August 18, 2020, according to the findings of a survey published in the Lancet Global Health.
Adult sero-prevalence increased approximately tenfold between May and August, 2020, said the survey that was funded by the Indian Council of Medical Research. The study, titled ‘SARS-CoV-2 antibody sero-prevalence in India, August-September 2020’, found that sero-prevalence was highest in urban slums.
The survey added that the lower infection-to-case ratio in August than in May reflected a substantial increase in testing across the country. Serum samples were collected from 29,082 individuals from 15,613 households between August 18-September 20, 2020.
The findings noted that the second nationwide serosurvey indicated that nearly 7% of India’s population aged 10 years or older had been exposed to SARS-CoV-2 infection by August, 2020, with an estimated 74 million infections. Sero-prevalence did not differ by age group or sex, but was higher in urban areas, especially in the slums, when compared to rural areas.
Sero-prevalence among adults increased by about ten times, from 0.7% in May to 7.1% in August. All 70 districts surveyed showed a rise in IgG seropositivity between the two serosurveys, although the change was highly variable.
The first serosurvey was done in May–June, 2020, among adults aged 18 years or older from 21 States. It found a SARS-CoV-2 IgG antibody sero-prevalence of 0.73% .
The sero-prevalence of 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 sero-conversion is associated with robust immunity.