Largest COVID-19 Contact Tracing Study Finds Children Key to Spread of Virus


This is the largest contact tracing study conducted in the world for any disease, analyzing the process of identifying people who came into contact with an infected person, according to a press release.

A new study of more than a half-million people who were exposed to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in India suggests that the continued spread of the virus is driven by a small percentage of those who become infected. Further, children and young adults were found to be potentially much more important to transmitting the virus, specifically within households, according to researchers from the United States and India.

Researchers from the Princeton Environmental Institute, Johns Hopkins University, and the University of California, Berkeley, worked with public health officials in the southeast Indian states of Tamil Nadu and Andhra Pradesh to track the infection pathways and mortality rate of 575,071 individuals who were exposed to 84,965 confirmed cases of coronavirus disease 2019 (COVID-19).

This is the largest contact tracing study conducted in the world for any disease, analyzing the process of identifying people who came into contact with an infected person, according to a press release.

Additionally, this is the first study to capture the extraordinary extent to which SARS-CoV-2 hinges on “superspreading,” in which a small percentage of the infected population passes the virus on to more people. The researchers found that 71% of infected individuals did not infect any of their contacts, whereas 8% of infected individuals accounted for 60% of new infections.

The data provide extensive insight into the spread and deadliness of COVID-19 in countries, such as India, that have a high incidence of resource-limited populations. The researchers found that COVID-19 deaths in India occurred 6 days after hospitalization compared with an average of 13 days in the United States. Further, deaths from COVID-19 in India have been concentrated among people 50 to 64 years of age, which is slightly younger than the 60 years of age and older population in the United States.

The researchers also reported the first large-scale evidence that the implementation of a countrywide shutdown in India led to substantial reductions in COVID-19 transmission. The chances of a person with COVID-19, regardless of age, passing it on to a close contact ranged from 2.6% in the community to 9% in the household. Children and young adults were especially key to transmitting the virus in the studied populations, according to the researchers.

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

In addition, children and young adults were much more likely to contract COVID-19 from people their own age. Across all age groups, people had a greater chance of catching COVID-19 from someone their own age. The overall probability of catching COVID-19 ranged from 4.7% for low-risk contacts up to 10.7% for high-risk contacts.


Largest COVID-19 contact tracing study to date finds children key to spread, evidence of superspreaders. Princeton University. Published September 30, 2020. Accessed September 30, 2020.

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