High Rate of Asymptomatic COVID-19 Infections Presents Challenge for Virus Containment

LA JOLLA, Calif. – Life-threatening respiratory distress is an all-too-common symptom of COVID-19, yet some infected with the virus seemingly have no symptoms at all. Still, it has not been clear how many people infected with the novel coronavirus are asymptomatic. To answer this question, scientists at the Scripps Research Translational Institute recently examined publicly available data on asymptomatic COVID-19 infections. Their study finds that nearly half of all people infected with the COVID-19 virus have no visible symptoms.

The researchers’ findings were based on an analysis of 16 publicly available datasets examining COVID-19 cases around the world. A wide variety of populations were studied, including nursing home residents, passengers on cruise ships, university students, and prison inmates. Though the individuals in these datasets varied in a number of ways (location, age, preexisting health conditions, race, etc.) they all had one thing in common: high rates of asymptomatic COVID-19 infections.

Researchers say prison inmates have a shockingly high rate of asymptomatic COVID-19 infections. Of the 3,000 inmates from prisons across four different states who tested positive for the virus, 96% of them were asymptomatic. This abnormally high rate of asymptomatic infections in prisons remains a mystery. The authors suggest that the transmission rate of other types of coronaviruses in prisons might be higher, leading to greater immunity to COVID-19 among inmates.

How do you fight something you can’t see?

It’s not entirely clear whether asymptomatic and symptomatic individuals have the same level of infectiousness. Previous studies have reported similar numbers of virus particles circulating in the bodies of asymptomatic individuals and symptomatic individuals, suggesting a similar potential to transmit the virus. Moreover, asymptomatic individuals may be able to transmit the virus for an extended period of time. Consequently, asymptomatic COVID-19 infections may pose a significant challenge to containing the virus.

Dr. Eric Topol, founder and director of the Scripps Research Translational Institute and a professor of molecular medicine suggests that the key to fighting COVID-19 will be widespread testing of individuals with and without apparent symptoms. “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 explains in a statement.

“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,” concludes lead author Daniel Oran. “So to protect others, we think that wearing a mask makes a lot of sense.”

The study is published in Annals of Internal Medicine.

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