Some health experts now believe as many as half of the people infected with the novel coronavirus (COVID-19) may not even be aware they are sick.
During a press conference on Sunday, the White House coronavirus task force’s Dr. Anthony Fauci said officials estimate “between 25 and 50 percent” of cases are asymptomatic, according to The New York Times. Fauci, 79, clarified that the range was only an estimate with differing opinions among the medical community.
Last week, the Centers for Disease Control and Prevention suggested that as many as one quarter of all infections don’t show symptoms.
The finding prompted officials to advise that everyone use face masks in public, since a person who seems healthy could be unknowingly spreading the contagious respiratory virus.
“One of the [pieces of] information that we have pretty much confirmed now is that a significant number of individuals that are infected actually remain asymptomatic,” CDC director Dr. Robert Redfield told NPR on Tuesday.
He added: “That’s important, because now you have individuals that may not have any symptoms that can contribute to transmission, and we have learned that in fact they do contribute to transmission.”
David Santiago/Miami Herald/Tribune News Service via Getty Two Miami residents wear gloves and protective masks as they put bags in the trunk of their car after shopping at a Walmart on Sunday.
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Redfield — who cautioned that COVID-19 is about three times as infectious as the flu — also said the CDC learned that those who do present symptoms are usually contagious up to 48 hours before symptoms appear, meaning they could be transmitting for days before realizing they have it.
“This helps explain how rapidly this virus continues to spread across the country,” he told NPR. “Because we have asymptomatic transmitters and we have individuals who are transmitting 48 hours before they become symptomatic.”
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Given the newly acquired knowledge about asymptomatic carriers, Redfield said the CDC is reviewing guidelines on face masks — after saying the general public does not need to wear masks unless they are feeling sick.
“Particularly with the new data, that there’s significant asymptomatic transmission, this is being critically re-reviewed to see if there’s potential additional value for individuals that are infected or individuals that may be asymptomatically infected [to wear face mask],” he said at the time. “I can tell you that the data and this issue of whether it’s going to contribute [to prevention] is being aggressively reviewed as we speak.”
According to data compiled by The New York Times, there have been more than 1.2 million confirmed cases and 70,000 deaths worldwide, as of April 6. In the United States, those tallies are 336,776 and 9,655, respectively.
As information about the coronavirus pandemic rapidly changes, PEOPLE is committed to providing the most recent data in our coverage. Some of the information in this story may have changed after publication. For the latest on COVID-19, readers are encouraged to use online resources from CDC, WHO, and local public health departments. To help provide doctors and nurses on the front lines with life-saving medical resources, donate to Direct Relief here.