COVID-19 risk twice as higher in urban slums; considerable population remains susceptible to infection

The risk of testing positive for COVID-19 was twice as high in urban slums compared to urban non-slum areas. The risk was the least in rural areas. Further, a considerable section of the population remains vulnerable to the virus. These were the main findings of the second national sero-survey, which was conducted by the Indian Council of Medical Research (ICMR) between August 17 and September 22.

In a sero survey, blood samples are collected from a general population and tested for IgG antibodies. If a person’s blood samples show the presence of IgG antibodies, it means that they were exposed to SARS CoV-2 virus, which causes COVID-19, sometime in the past.

The second survey observed that the risk of infection in urban slums was at 15.6% as compared to the non-slum areas (8.2%) in the same urban centres. The risk at these slums was four times the risk in rural areas (4.4%).

The sero-survey highlighted that one in 15 people (aged 10 and above) had in all likelihood been exposed to the virus by the end of August.

"Of 29,082 people surveyed, only 6.6% above the age of 10 showed evidence of past exposure to SARS-COV2," Dr Balram Bhargava, Director General of ICMR said. The prevalence of infection above the age of 18 was 7.1%. Just as it was in the first survey, the national prevalence of the infection was found to be 0.73%.

The second sero-survey was conducted across the same 700 villages and (urban) wards from 70 districts in 21 states visited for the first survey (which was conducted between May 11 and June 4). In the first study, 30,283 households were surveyed, and 28,000 individuals had enrolled.

The first survey had found that sero-positivity was highest in villages (rural areas) at 69.4% compared to 15.9% in urban slums and 14.6% in non-slums. However, in that survey only 25.9% (a fourth) of the surveyed clusters were from urban areas.

The worst-affected were those between the age group of 18 and 45 years, as 43.3% had developed antibodies against SARS-CoV-2.

For every confirmed COVID-19 case in August, there were at least 26 to 32 infections that went undetected. The detection of cases improved, the government said, because of increased contact tracing and tracking. In the first survey, the missed cases number stood between 81-130. This survey found that the prevalence of the virus was not different by age group or gender.

Delhi recorded a 29.1% sero-prevalence in the second round, which was conducted between August 1 and 7. This was higher than the 23.1% recorded in the first round conducted between June 27 and July 10.

Mumbai had the highest sero-prevalence with 57.8% of samples (from slums) testing positive, but it was 17.4% for samples from non-slum areas.

This was followed by Puducherry, which showed a sero-prevalance of 22.7% during the second round of the survey between September 10 and 16.

In the first phase of the sero-survey during August 11-16, Puducherry had shown a sero-prevalence of only 4.9%. Chennai recorded a sero-prevalence of 21.5%, Ahmedabad 17.6% and Indore in Madhya Pradesh registered 7.8% in the survey.

The second sero-survey also wants to drive home the point that the early, unplanned lockdown from March 24, which cause untold misery to lakhs of Indians, had checked the spread of SARS-CoV-2 virus. These grim figures point to the fact that herd immunity is a distant dream for the country.