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How Many People With the Coronavirus Are Asymptomatic?

The Cut logo The Cut 4/7/2020 Amanda Arnold

© Guido Mieth/Getty Images Last week, the Centers for Disease Control and Prevention issued new face-mask guidance, encouraging everyone to wear cloth face coverings when in public. The reasoning: “We now know from recent studies that a significant portion of individuals with coronavirus lack symptoms,” and that those individuals can transmit the virus to others.

While we don’t know for certain what percentage of people infected with the coronavirus are asymptomatic, we know that the percentage isn’t insignificant. It’s why elected officials across the world have stressed the importance of staying home as much as possible, largely to help protect essential workers who can’t. Seeing as the U.S. doesn’t have widespread testing, it’s unlikely we’ll ever get a good picture of exactly how many cases Stateside are asymptomatic. But here’s what we know about asymptomatic carriers so far.

Just to be clear: What exactly does it mean to be asymptomatic?

If you are truly asymptomatic that means you are infected with a virus, but you never exhibit symptoms of disease. In the case of the coronavirus, those common symptoms would be dry cough, fever, and fatigue. However, as health officials have repeatedly stressed in an attempt to convince people to adhere to strict social-distancing measures, people with the coronavirus who are asymptomatic are still contagious.

How many people with the coronavirus are asymptomatic?

Here’s where we’re lacking conclusive research. This past week, one lab in Iceland reported that as many as 50 percent of cases could be asymptomatic. An analysis of the confirmed coronavirus cases aboard the Diamond Princess cruise found that 18 percent of the infected passengers were asymptomatic. Last week, the CDC director Dr. Robert Redfield estimated that 25 percent of people with the coronavirus may be asymptomatic. Most recently, National Institute of Allergy and Infectious Diseases director Dr. Anthony Fauci estimated that 25 to 50 percent of cases may be asymptomatic.

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Is it possible that some people who were asymptomatic when they were tested later showed symptoms?

Absolutely. Dr. Maria Van Kerkhove, head of the emerging diseases and zoonoses unit at the World Health Organization, told ProPublica she thinks that many cases have been misclassified as asymptomatic, when in fact they were “presymptomatic.” (People who are presymptomatic have no symptoms when they test positive, but go on to develop symptoms.)

“Most of the people who were thought to be asymptomatic aren’t truly asymptomatic,” she said. “When [WHO] went back and interviewed them, most of them said, ‘Actually, I didn’t feel well, but I didn’t think it was an important thing to mention. I had a low-grade temperature, or aches, but I didn’t think that counted.’” Some examples of this have been documented: The CDC, for example, found that of the 13 patients in a nursing facility in Washington who reported no symptoms when they tested positive for the coronavirus, 10 went on to later develop symptoms.

However, Dr. Jeffrey Shaman, an infectious-diseases expert at Columbia University, has cautioned against spending too much time on the semantics debate between asymptomatic and presymptomatic, telling the New York Times, “The bottom line is that there are people out there shedding the virus who don’t know that they’re infected.”

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