Scientists Say An Estimated 86 Percent Of People With Coronavirus Don’t Know It, Driving Infections

A security police officer controls the temperature of a government official at the entrance to the La Moneda presidential palace as the Chilean government takes measures to control the spread of the coronavirus on March 17, 2020 in Santiago, Chile.
Marcelo Hernandez / Getty Images

As the coronavirus continues to spread, scientists say that part of the challenge of limiting the pandemic is that a vast majority of infected people don’t know they have the virus. According to a new study published in the journal Science, there appear to be a high rate of undocumented infections — or “stealth” cases — that are driving the rapid spread of the disease.

Researchers looked at infections in Wuhan, China, where the virus is thought to have begun, before the travel ban was implemented. They note that six out of seven people during that time were unaware that they were infected, either because they had no symptoms or mild symptoms.

While undocumented infections appear to be less contagious than those with worse symptoms, it’s the undocumented cases that are responsible for a vast majority — 79 percent — of subsequent infections.

“These undocumented infections often experience mild, limited or no symptoms and hence go unrecognized, and, depending on their contagiousness and numbers, can expose a far greater portion of the population to virus than would otherwise occur,” the report states.

The study’s co-author, Jeffrey Shaman from Columbia University, says that the study highlights the importance of social distancing.

“This is different than what we’re used to seeing in Western democratic societies,” he told the Mercury News. “This virus thrives on people mingling and meeting each other.”

The report says that it’s likely that this rate of undetected cases matches what was seen in the U.S. and Europe before travel restrictions and social distancing measures were put in place.

These “stealth” cases will likely continue to be one of the biggest challenges to containing the virus.

“People may not recognize it. Or they think they have a cold,” Shaman said.

Though these people may be unaware, they can spread the disease to other people who may come down with a much more severe case.

When applied to the U.S., these findings could mean that there are far more cases than have been reported. This is especially true given the limitations of testing, currently. Instead of the 1,629 infections as of Monday, there could be closer to 13,000.

Containing these stealth cases is one of the most important elements of limiting the disease, which has killed thousands and has rocked the global economy, with some experts predicting a looming recession.

“It will continue to present a major challenge to the containment of this outbreak going forward,” Shaman said.

He added that until mass testing is available, countries won’t be able to proactively determine who has the virus.

“We’re seeing just the tip of the iceberg,” he concluded.