Children and young adults have more propensity to transmit novel coronavirus, especially within households, according to a research study which tracked the infection pathways in Andhra Pradesh and Tamil Nadu, the States that reported second and third highest Covid-19 cases after Maharashtra.

The study carried out by researchers from the Princeton Environmental Institute (PEI), Johns Hopkins University and the University of California Berkeley in collaboration with public health officials in these States also showed that the virus continued spread was driven by only a small percentage of those who become infected. The study involved more than half a million people appeared in the prestigious journal Science on Wednesday.

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 Covid-19 hinges on “superspreading”, in which a small percentage of the infected population passes the virus on to more people. The researchers found that 71 per cent of infected individuals did not infect any of their contacts, while a mere 8 per cent of infected individuals accounted for 60 per cent of new infections.

“Our study presents the largest empirical demonstration of superspreading that we are aware of in any infectious disease,” Laxminarayan said. “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,” he said in a statement.

Lockdown impact

The study also confirmed that the implementation of the nation-wide lockdown in the initial days of the pandemic led to substantial reduction in coronavirus transmission.

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 per cent in the community to 9 per cent 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 resource-limited 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."

They found that coronavirus-related deaths in India occurred, on average, six days after hospitalisation compared to an average of 13 days in the US. Also, deaths from coronavirus in India have been concentrated among people aged 50-64, which is slightly younger than the 60-plus at-risk population in the US. Similarly, in Andhra Pradesh and Tamil Nadu only 17.9 per cent of Covid-19 deaths occurred before August were among people older than 75 as compared to 58.1 per cent Covid-19 deaths in the US, the study said.

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