New studies in several countries and a large coronavirus outbreak in Massachusetts bring into question reassuring assertions by US officials about the way the novel virus spreads.
These officials have emphasized that the virus is spread mainly by people who are already showing symptoms, such as fever, cough or difficulty breathing. If that’s true, it’s good news, since people who are obviously ill can be identified and isolated, making it easier to control an outbreak.
But it appears that a Massachusetts coronavirus cluster with at least 82 cases was started by people who were not yet showing symptoms, and more than half a dozen studies have shown that people without symptoms are causing substantial amounts of infection.
For weeks, federal officials have emphasized that asymptomatic transmission can happen, but have said that it’s not a significant factor in the spread of the virus.
On March 1 on ABC’s This Week, US Secretary of Health and Human Services Alex Azar told host George Stephanopoulos that asymptomatic spread is “not the major driver” of the spread of the new coronavirus.
“You really need to just focus on the individuals that are symptomatic,” he said. “It [the containment strategy] really does depend on symptomatic presentation.”
The website for the US Centers for Disease Control and Prevention echoes that assessment.
“Some spread might be possible before people show symptoms; there have been reports of this occurring with this new coronavirus, but this is not thought to be the main way the virus spreads,” according to the website.
But during a press briefing at the White House on Saturday, the administration’s coronavirus response coordinator, Dr. Deborah Birx, seemed to strike a somewhat different note on asymptomatic transmission.
She said they’re trying to understand people under the age of 20 who don’t have “significant symptoms” — “Are they a group that are potentially asymptomatic and spreading the virus?” she asked.
“Until you really understand how many people are asymptomatic and asymptomatically passing the virus on, we think it’s better for the entire American public to know that the risk of serious illness may be low, but they could be potentially spreading the virus to others.
“That’s why we’re asking every American to take personal responsibility to prevent that spread.”
Several experts said while it’s unclear exactly what percentage of the transmission in the outbreak is fueled by people who are obviously sick versus those who have no symptoms or very mild symptoms, it’s become clear that transmission by people who are asymptomatic or mildly symptomatic is responsible for more transmission than previously thought.
“We now know that asymptomatic transmission likely [plays] an important role in spreading this virus,” said Michael Osterholm, director of the Center for Infectious Disease Research and Policy at the University of Minnesota.
Osterholm added that it’s “absolutely clear” that asymptomatic infection “surely can fuel a pandemic like this in a way that’s going to make it very difficult to control.”
In an article two weeks ago in the New England Journal of Medicine, Bill Gates, co-chair of the Bill and Melinda Gates Foundation, expressed concern about the spread of the disease by people who haven’t yet developed symptoms, or who are only a bit sick.