Coronavirus is spread primarily by a small group of infected people, especially children and young adults, according to the conclusions of the largest contact-tracing study carried out to date.
The study of more than half a million people in India found that just 8 percent of people infected with COVID-19 had spread the virus to over 60 percent of the new infections detected.
These results highlight the role of superspreaders – people who infect a large number of others with a disease.
“Superspreading events are the rule rather than the exception when one is looking at the spread of COVID-19, both in India and likely in all affected places,” said lead researcher Ramanan Laxminarayan, from the Princeton Environmental Institute (PEI).
In contrast, 71 percent of the cases did not have any secondary cases linked to them, suggesting that the majority of people with COVID-19 do not spread it.
Researchers also found that children and young adults were especially prominent in spreading the virus.
“We identify high prevalence of infection among children who were contacts of cases around their own age; this finding of enhanced infection risk among individuals exposed to similar-age cases was also apparent among adults,” wrote the researchers.
Researchers from PEI, Johns Hopkins University, and the University of California-Berkeley coordinated with officials in the southeastern Indian states of Tamil Nadu and Andhra Pradesh to carry out the study.
They used contact-tracing – the process of identifying people who came into contact with a COVID-19 case – to track the spread of coronavirus in the two Indian states. The study considered 575,071 people who had been exposed to the 84,965 confirmed cases in the province.
While the study said that contact-tracing has its limitations and may not be representative of the full population, it recommended further research using the technique to help slow the spread of the virus.
“Surveillance and contact tracing are critical components of an effective public health response to COVID-19,” it said.