Dr. Topol and Oran reviewed the data of SARS-CoV-2 studies that included clear information about testing methods for diagnosing infection with the virus.
They ended up assessing studies of 16 different cohorts, including groups of cruise ship passengers, prison inmates, and nursing home residents tested for COVID-19.
“What virtually all of them had in common was that a very large proportion of infected individuals had no symptoms,” notes Oran commenting on the findings.
“Among more than 3,000 prison inmates in four states who tested positive for the coronavirus, the figure was astronomical: 96% asymptomatic,” he emphasizes.
Looking at all the data together, the investigators estimated that around 40–45% of people contracting the new coronavirus are likely to be asymptomatic.
They also inferred that people who showed no COVID-19 symptoms were, nevertheless, liable to spread the virus over 14 days or more after infection.
“The silent spread of the virus makes it all the more challenging to control,” notes Dr. Topol.
“Our review really highlights the importance of testing. It’s clear that with such a high asymptomatic rate, we need to cast a very wide net; otherwise, the virus will continue to evade us,” he adds.
Still, Dr. Topol and Oran note that it remains difficult to tell just how likely it is for asymptomatic people to spread the virus further, even though both symptomatic and asymptomatic individuals present similar viral loads.
To find out, the researchers explain, we would need access to more longitudinal studies with representative cohorts of asymptomatic individuals. For the current review, the researchers were able to obtain longitudinal data on only five cohorts.