Researchers on Wednesday said that the transmission of the coronavirus in India has been mainly driven by super-spreaders, PTI reported. The World Health Organization describes “super-spreading” as incidents of transmission where a large number of people can become infected from a common source.

A contact tracing study, said to be the largest epidemiological analyses conducted in the world, was published in the journal Science. The researchers, including those from Tamil Nadu and Andhra Pradesh, found that over 70% of infected patients in the country did not pass the disease to any of their contacts, while 8% of infected individuals accounted for 60% of new infections.

The study assessed the infection transmission patterns in 5,75,071 individuals, who were exposed to 84,965 confirmed coronavirus cases, in Tamil Nadu and Andhra Pradesh. Data for the study was gathered by thousands of contact-tracers during the nationwide lockdown to rein in the infection. Both the states account for about 10% of the country’s population.

Ramanan Laxminarayan, director of the Center for Disease Dynamics, Economics and Policy in New Delhi, who wrote the study, said it offers a peek into the pandemic’s trajectory in a low-and middle-income country. He added that most research on the pandemic has come from China, Europe and North America, but cases are now increasing rapidly in India and other developing countries, according to Bloomberg.

“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 contrast with the super-spreader minority, 71% of confirmed cases whose contacts were traced weren’t found to have spread the virus to anyone.”

It revealed that children are more efficient transmitters of the virus than initially believed. Researchers found children under 14 to be frequent “silent” spreaders of the virus, especially to their parents and friends. “This shows that even without schools being functional, children-to-children transmission seems to be quite important,” Laxminarayan said. “As terrible as it is to say – with two kids at home myself – it’s actually important to keep the kids home.”

Among other trends, the study also found that both cases and deaths due to the coronavirus have been more heavily concentrated in the 40-69 year age group in India than what is seen in high-income countries.

“The results on disease transmission and mortality have the potential to inform policy to fight Covid-19,” Laxminarayan added. “The study also speaks to the capacity of research emerging from India to help inform the global response to Covid-19.”

Both Andhra Pradesh and Tamil Nadu, which reported their first SARS-CoV-2 infections on March 5, are among the Indian states with the largest healthcare workforce and public health expenditures per capita, the study said. It said 63% of those who died had at least one co-morbidity, and 36% had two or more underlying health conditions that made them more susceptible to the infection. Meanwhile, about 45% of those who died were diabetic.

The researchers, who were also from Princeton University and Johns Hopkins Bloomberg School of Public Health, also found that infected people spread the virus via prolonged close contact on buses and other forms of transportation. According to them, there was a 79% chance of an infection occurring in such settings.

The second national sero-survey by the Indian Council of Medical Research showed that one in 15 people, aged over 10 years, may have been exposed to the coronavirus by August-end. The findings, revealed on Tuesday, also revealed that a considerable section of the population is still vulnerable.

India’s coronavirus case tally increased by 86,821 in the last 24 hours to 63,12,584, data from the health ministry showed. Deaths from coronavirus infections rose by 1,181 to 98,678. The government has eased more restrictions and allowed cinema halls to reopen at 50% capacity.