Largest COVID contact-tracing study finds children, young adults are most common ‘superspreaders’

PRINCETON, N.J. — In the United States, certain regions are using contact-tracing to find out where potential coronavirus patients are going and who they might expose. In the largest COVID study to date, an entire country is using contact-tracing to reveal who might be most likely to spread the virus. A team from the U.S. and India find children and young adults have the highest chances of being branded as “superspreaders.”

The review of southeast Indian states of Tamil Nadu and Andhra Pradesh examines infection and mortality rates among 575,071 people. This group was exposed to 84,965 confirmed cases of COVID-19. Researchers believe, at this point, coronavirus is only being spread by a small portion of infected patients.

Lead researcher Ramanan Laxminarayan from the Princeton Environmental Institute says 71 percent of COVID-positive patients in the study did not infect any of people they came in contact with. Meanwhile, a mere eight percent of COVID-19 carriers are responsible for 60 percent of new infections.

“Our study presents the largest empirical demonstration of superspreading that we are aware of in any infectious disease,” Laxminarayan says in a university release. “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.”

Who is spreading coronavirus to whom?

While some groups are more likely to spread the virus than others, the study finds most patients with COVID infect someone around their own age. Children and young adults were found to be at the top of this list.

“Kids are very efficient transmitters in this setting, which is something that hasn’t been firmly established in previous studies,” Laxminarayan explains. “We found that reported cases and deaths have been more concentrated in younger cohorts than we expected based on observations in higher-income countries.”

Study authors add, regardless of age, the overall chance of contracting coronavirus ranges from 4.7 percent in low-risk contacts to 10.7 percent for high-risk encounters. The report finds the chance of becoming infected with COVID also depends on where you meet a carrier.

The Indian contact-trace found patients only had a 2.6 percent chance of passing on the virus during close contact when out in the community. That risk rose to nine percent while inside a home. As for the “superspreaders,” children and young adults made up one in three COVID-19 cases in the report.

National differences

The results also show subtle differences in who’s getting sick in the U.S. and India. Researchers find deaths caused by the pandemic were not only occurring faster, but also in younger Indian residents.

The country, which the study notes has a high number of resource-limited populations, has suffered more than 96,000 deaths due to the illness. The fatalities are occurring, on average, six days after a patient enters the hospital. That number is around 13 days in the United States, which has seen over 200,000 deaths attributed to coronavirus. Most Indian deaths in the study were found to be among 50 to 64-year-old patients, slightly younger than the U.S. average.

The large-scale review also finds evidence that a nationwide shutdown led to a significant decrease in COVID transmissions. India has a population of about 1.35 billion people.

The study appears in the journal Science.

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