About 8% of super-spreaders responsible for two-thirds of COVID cases in India, says study

A small group that included only 8% of India’s confirmed cases spread the infection to almost two-thirds of people who contracted the disease, say researchers

Serum Institute of India is the world’s largest vaccine producer by volume. Representational photo: iStock

A small group of patients was responsible for spreading the coronavirus to almost two-thirds of the total number of patients who were affected by COVID-19 in India, the country with the largest number of cases behind the US, researchers have found in the first major study on the virus and its impact on population in a developing country.

This group of coronavirus super-spreaders included about 8% of India’s confirmed cases, according to a study that appeared in the journal Science on Wednesday, Bloomberg reported.

The research involved tracking more than 30 lakh people who had come into contact with COVID patients. It was conducted till August 1, much before the pandemic reached a peak, in the south Indian states of Andhra Pradesh and Tamil Nadu. The two states have a population of about 13 crore, or about 10% of India’s. The first case in both Andhra Pradesh and Tamil Nadu were reported on March 5.

The researchers found most infections happened when people used public transport like buses, where they were exposed to an infected person for a prolonged period.

The study involved analysis of comprehensive surveillance and contact tracing data for 575,071 tested contacts of 84,965 infected individuals, with epidemiological data overlaid.

The researchers found that instead of higher mortality in age group greater than 85 as seen in developed nations, mortality in India plateaus at 65. This is after statistically adjusting for the lower age demographics of India overall. They have said this can be explained throughsurvivorship bias — that most in the older age group in India might be from a high-income background and better socio-economic strata with   access to high-end healthcare.

This is also one of the first studies to state that infected children also  transmit the disease just like adults. Researchers found children under 14 to have been “silent” spreaders of the virus especially to their parents.

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The coronavirus has been rapidly spreading in India, with the number of cases exploding to 63 lakh at the end of September from about 36 lakh at the beginning of the month.

In contrast to the small group of super-spreaders, a majority of the patients — about 71% — did not spread the disease to anyone. This was again ascertained by tracing their contacts, the study said.

India is now among the many developing countries where cases are increasing at a fast clip, the researchers led by Ramanan Laxminarayan, director of the Center for Disease Dynamics, Economics & Policy, said. They said most of the research on the pandemic had so far been happening in places like China, Europe and North America.

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The study said the fatality rate in developing countries could be high because the populations face huge hurdles in accessing medical care.

“We’ve never had this degree of information to say, hey, some people are really transmitting the virus in a massive way,” Laxminarayan said in an interview, Bloomberg reported.

He said those involved in the research got in touch with up to about 80 contacts of each confirmed case they studied. The researchers came from various institutions, including Princeton University and Johns Hopkins Bloomberg School of Public Health in the US, besides those in India.

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