Role of Asymptomatic Infections in COVID-19 Spread

Role of Asymptomatic Infections in COVID-19 Spread

Research suggests that asymptomatic infections may have played a role in the early and continuing spread of COVID-19.


Recent study findings published in Annals of Internal Medicine indicate that asymptomatic infections may account for as many as 45% of all COVID-19 cases. The analysis, conducted by researchers at Scripps Research Institute in La Jolla, California, notes that asymptomatic cases may play a role in the spread of the virus and suggests the need for testing and contact tracing to mitigate the pandemic.

“The silent spread of the virus makes it all the more challenging to control,” said Eric Topol, MD, founder and director of the Scripps Research Translational Institute and professor of molecular medicine at the Institute. “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.”

Topol, in conjunction with Daniel P. Oran, associate director of the Scripps Research Translational Institute, gathered information from testing studies on 16 diverse cohorts from around the globe. The datasets included data on nursing home residents, cruise ship passengers, prison inmates and various other groups. “What virtually all of them had in common was that a very large proportion of infected individuals had no symptoms,” said Oran. Among more than 3,000 prison inmates in four states who tested positive for the coronavirus, the figure was astronomical: 96% asymptomatic.”

Additionally, the analysis indicated that asymptomatic individuals are able to transmit the virus for an extended period, perhaps longer than 14 days. Because it’s unclear whether the infectiousness reaches the same levels in all asymptomatic subjects, large-scale studies of larger numbers of asymptomatic people are necessary. Researchers also concluded that the absence of symptoms may not necessarily imply that no physical damage occurred. CT scans on 54% of 76 asymptomatic individuals on a particular cruise ship appeared to indicate significant lung abnormalities. Additional research is necessary to confirm the possible significance of the finding.

“Our estimate of 40% to 45% asymptomatic means that, if you’re unlucky enough to get infected, the probability is almost a flip of a coin on whether you’re going to have symptoms. So to protect others, we think that wearing a mask makes a lot of sense,” Oran said.


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