Study Finds ‘Silent Transmission’ of Virus by People Without Symptoms

(CN) – A new study of coronavirus cases in China has found what a Texas university describes as the strongest evidence yet that people are spreading the new virus and the disease it causes before they ever show symptoms.

The study, performed by a global team of researchers in China, France and at the University of Texas in Austin, analyzed 468 confirmed cases of the COVID-19 disease that were reported from late January to early February in 93 Chinese cities.

They found that in about 12% of those cases, people without symptoms passed the virus on to another person, a finding that further bolsters the argument from health experts that “social distancing” is a crucial tool in fighting the virus.

President Donald Trump on Monday announced new national guidelines for slowing the spread of the virus, encouraging the public to avoid social gatherings of more than 10 people and avoid eating or drinking at bars and restaurants.

A cyclist wears a mask as he crosses the Brooklyn Bridge in New York City on Monday. (AP Photo/Mark Lennihan)

The guidelines include recommendations that adults and schoolchildren alike do their work from home “whenever possible.”

“This [study] provides evidence that extensive control measures including isolation, quarantine, school closures, travel restrictions and cancellation of mass gatherings may be warranted,” Lauren Ancel Meyers, a University of Texas biology professor and author on the study, said in a statement.

“Our findings are corroborated by instances of silent transmission and rising case counts in hundreds of cities worldwide,” Meyers said. “This tells us that COVID-19 outbreaks can be elusive and require extreme measures.”

While containment efforts have played out at the local level across the country, the White House has so far appeared reluctant to launch more draconian lockdowns like those seen in Italy, where more than 2,000 people have so far died from the disease.

“There are some places in our nation that are not very affected at all,” President Trump said Monday, pushing back on a report from CNN that some within his administration were discussing the possibility of a nationwide curfew.

“We may look at certain areas, certain hotspots, as they call them — we’ll be looking at that. But at this point no we’re not,” the president said.

Monday’s study, which is pending publication in the journal Emerging Infectious Disease, also found that the novel coronavirus spreads in a “chain of transmission” relatively quickly, in just four days.

The team landed on that number by calculating a “serial interval” for the virus, defined as the time between when an already-infected person develops symptoms and when a second person who’s become infected by the first person shows symptoms.

“Ebola, with a serial interval of several weeks, is much easier to contain than influenza, with a serial interval of only a few days. Public health responders to Ebola outbreaks have much more time to identify and isolate cases before they infect others,” Meyers said. “The data suggest that this coronavirus may spread like the flu. That means we need to move quickly and aggressively to curb the emerging threat.”

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