Researchers from the Princeton Environmental Institute (PEI), 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 COVID-19, the disease caused by SARS-CoV-2. It is the largest contact tracing study — which is the process of identifying people who came into contact with an infected person — conducted in the world for any disease.
Lead researcher Ramanan Laxminarayan, a senior research scholar in PEI, said that the paper is the first large 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, while a mere 8% of infected individuals accounted for 60% of new infections…
The researchers found that the chances of a person with coronavirus, regardless of their age, passing it on to a close contact ranged from 2.6% in the community to 9% in the household. The researchers found that children and young adults — who made up one-third of COVID cases — were especially key to transmitting the virus in the studied populations.
“Kids are very efficient transmitters in this setting, which is something that hasn’t been firmly established in previous studies,” Laxminarayan said. “We found that reported cases and deaths have been more concentrated in younger cohorts than we expected based on observations in higher-income countries.”