A serological survey conducted by scientists of the Indian Council of Medical Research has found that India had an estimated 64 lakh coronavirus cases by early May, PTI reported. The paper underwent peer review and was published in the Indian Journal of Medical Research on Thursday.
The survey, conducted between May 11 and June 4 in 21 states, suggested that 0.73% adults in India were exposed to the infection. This was the first of its kind survey and was followed up by smaller surveys commissioned by states. The findings show that for every confirmed case in May, there were 82-130 infections that went undetected. As of Friday, India has recorded 45,62,414 total cases and 76,271 deaths.
The survey tested blood samples of 28,000 individuals and showed that sero positivity was highest in the age group of 18 to 45 years at 43.3%. This was followed by those between 46 and 60 years at 39.5% and was the lowest among those above 60 with 17.2% positivity.
A total of 64,68,388 adult infections were estimated in India by early May, the survey report said.
Serology tests “look for antibodies in blood”, according to the United States’ Centers for Disease Control and Prevention. “If antibodies are found, that means there has been a previous infection,” it says. “However, there is a chance a positive result means that you have antibodies from an infection with a virus from the same family of viruses (called coronaviruses), such as the one that causes the common cold.”
Serological surveys show the number of people that may have been infected with the coronavirus in an area. However, they do not show how many are immune to the virus. It is still unclear how long antibodies last in infected persons and how many antibodies are required to protect a person from reinfection.
“The findings of our survey indicated that the overall seroprevalence in India was low, with less than 1% of the adult population exposed to SARS-CoV-2 by mid-May 2020,” Thursday’s report said. “The low prevalence observed in most districts indicates that India is in early phase of the epidemic and the majority of the Indian population is still susceptible to SARS-CoV-2 infection. It is, therefore, necessary to continue to implement the context-specific containment measures including testing of all symptomaties, isolating positive cases and tracing high-risk contacts to slow transmission and to prevent the overburdening of the health system.”
Meanwhile, the survey also showed that between May and June, coronavirus cases had spread to rural India. The sero positivity was highest at 69.4% in the rural areas, while in the urban slums it was 15.9% and in urban non-slums it was recorded at 14.6%, according to IANS. About one-fourth or 25.9% of the surveyed clusters were from urban areas, the report said.
The survey also noted that the under-detection of coronavirus cases in the zero stratum – or places where there is a zero or low incidence of cases – could be on account of low testing as well as poor access to testing laboratories. In four of the 15 districts in this stratum, testing laboratories were not available in district headquarters and the samples were transported to the state headquarter hospitals for diagnosis, it added.
Andhra Pradesh sero survey
A sero survey conducted in Andhra Pradesh has revealed that 20% of the 5.34 crore population of the state has acquired immunity to the coronavirus. In August, the survey conducted in two phases with a sample size of 5,000 in each of the 13 districts showed that 19.7% of people developed antibodies for SARS-CoV-2, the infection-causing virus.
Andhra Pradesh Commissioner for Health and Family Welfare Katamaneni Bhaskar said 22.5% population in urban areas and 18.2% in rural areas has acquired immunity. Of the total surveyed, 19.9% women and 19.5% men have developed antibodies, Bhaskar said at a press conference on Thursday.
The findings also revealed that 90% to 100% of the positives were asymptomatic. “Sero surveillance provides estimates of antibody levels against infectious diseases and is considered a gold standard for measuring population immunity,” Bhaskar said. “We have completed one round of surveillance in all districts in two phases.”