New Study Shows How Much Asymptomatic People Spread COVID-19

Since the coronavirus pandemic began, scientists and public health experts have been puzzled by the role of asymptomatic spread. How many people have COVID-19, but no (or virtually no) symptoms? And to what extent do those silent carriers contribute to the spread of the virus?

Early estimates ran the gamut, but researchers are now settling on a much clearer number.

A new model published in the journal JAMA Open Network this week, developed by researchers with the Centers for Disease Control and Prevention, suggests that more than half of total COVID-19 transmissions come from those who have no symptoms. In other words, the majority of the spread is from silent carriers.

Experts have been eager to better understand the issue of asymptomatic spread because the pandemic is harder to contain if people go out and infect others without realizing they themselves are ill.

But one challenge has been that the term is not specific, said Eili Klein, an associate professor in the department of emergency medicine with Johns Hopkins University.

“There has been a definitional issue,” Klein, who was not affiliated with the study, told HuffPost. “What does ‘asymptomatic’ mean?”

For example, some people are pre-symptomatic and may spread the virus before they realize they are ill. Others may never develop any symptoms (or have symptoms so mild they miss them altogether) but nonetheless pass the virus along, explained Klein.

The new model suggests that both of those groups seem to play a key role in the spread of COVID-19.

About 35% of the asymptomatic spread comes from people in that pre-symptomatic group, while 24% comes from those who never develop symptoms.

And that means that some current screening efforts — like regular temperature checks or testing programs that largely target individuals who are seriously ill — are likely to miss many silent carriers.

That is why the researchers behind the new study call for “strategic testing of people who are not ill.” That includes anyone who has been exposed to a person who has tested positive for COVID-19, as well as widespread testing for people who are at a higher risk of exposing others.

But Klein said that another crucial piece of the puzzle is contact tracing, which has been widely underused and largely ineffective in the United States. That makes it difficult to truly grasp how the virus is passing among people who have no symptoms.

“It’s really hard to know for sure what is happening without really good contact tracing,” Klein said. “But I think there’s enough well-documented cases of people who are asymptomatic, transmitting to lots of people, to say that it probably plays a big role in this process.”

Perhaps above all, the new model clearly reinforces the need for proven public health measures, like universal masking, hand-washing and social distancing — all of which protect people against the silent spread of COVID-19.