At least 50% of Covid-19 cases are asymptomatic, study suggests

Prashasti Awasthi Mumbai | Updated on February 12, 2021

Non-symptomatic cases contributed substantially to community transmission

Researchers at the University of Chicago found that during the initial wave of the Covid-19 outbreak in New York City, only one in five to one in seven cases of the virus was symptomatic.

According to the research team, the non-symptomatic cases contributed substantially to community transmission. They made up at least 50 per cent of the driving force of the coronavirus infection.

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First author Rahul Subramanian, a Ph.D. student of epidemiology at UChicago, stated: "Without testing capacity data, it's very difficult to estimate the difference between cases that were unreported due to a lack of testing and cases that were actually asymptomatic."

He added: "We wanted to disentangle those two things, and since New York City was one of the first cities to report the daily number of tests completed, we were able to use those numbers to estimate how many Covid-19 cases were symptomatic."

Senior author Mercedes Pascual, the Louis Block Professor of Ecology and Evolution at UChicago, revealed that their study showed the proportion of individuals who are symptomatic for Covid-19 is between 13 per cent and 18 per cent.

“Regardless of the uncertainty in all other parameters, we can tell that more than 50 per cent of the transmission happening in the community is from people without symptoms — those who are asymptomatic and pre-symptomatic," he further noted.

This data analysis however, does not indicate how infectious asymptomatic individuals are, nor account for the new variants of the virus currently spreading in the US.

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"Even if asymptomatic people aren't transmitting the virus at high rates, they constitute something like 80 per cent of all infections," said co-author Qixin He, an assistant professor at Perdue University.

The findings of the study were published in the Proceedings of the National Academy of Sciences.

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Published on February 12, 2021
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