The study, based on a giant contact tracing effort involving more than 3 million people in India, shows that most Covid-19 patients have never infected anyone else. The researchers found that 70% of those infected did not infect any of their contacts, while 8% of patients accounted for 60% of the new infections observed.
The study also contradicts the widely held belief that children are unlikely to catch the coronavirus.
“While the role of children in transmission has been debated, we identify a high prevalence of infection in children who were case contacts around their own age,” the team wrote in its report, published in the journal Science.
“We were surprised to find that only 8% of the primary infected cases were responsible for 60% of the infected contacts,” he said. “It’s an extremely disproportionate effect. Super broadcast has been suspected, but not fully documented. Most of the index cases – the first patient in a chain of transmission – were adults between the ages of 20 and 45, according to the team.
“The young to middle-aged adulthood group is the one who comes into contact with people. These are the people most likely to be outside the home. They are the ones who carry the disease from one place to another, ”Laxminarayan said.
The study also showed that the locks worked. The restrictions reduced the rate of transmission, the team found. Case fatality ratios, a measure of the death rate, have also declined over time. “Those who tested positive in May and June were 13% less likely to die than those tested in March and April,” Laxminarayan said.