Infectious disease researchers at The University of Texas at Austin
studying the novel coronavirus were able to identify how quickly the virus can
spread, a factor that may help public health officials in their efforts at
containment. They found that time between cases in a chain of transmission is
less than a week and that more than 10% of patients are infected by somebody
who has the virus but does not yet have symptoms.
In the paper in press with the journal Emerging Infectious Diseases, a
team of scientists from the United States, France, China and Hong Kong were
able to calculate what’s called the serial interval of the virus. To measure
serial interval, scientists look at the time it takes for symptoms to appear in
two people with the virus: the person who infects another, and the infected
second person.
Researchers
found that the average serial interval for the novel coronavirus in China was
approximately four days. This also is among the first studies to estimate the
rate of asymptomatic transmission.
The speed of an
epidemic depends on two things — how many people each case infects and how long
it takes for infection between people to spread. The first quantity is called
the reproduction number; the second is the serial interval. The short serial
interval of COVID-19 means emerging outbreaks will grow quickly and could be
difficult to stop, the researchers said.
“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,” said Lauren Ancel Meyers, a professor of integrative biology at UT
Austin. “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.”
Meyers and her
team examined more than 450 infection case reports from 93 cities in China and
found the strongest evidence yet that people without symptoms must be
transmitting the virus, known as pre-symptomatic transmission. According to the
paper, more than 1 in 10 infections were from people who had the virus but did
not yet feel sick.
Previously,
researchers had some uncertainty about asymptomatic transmission with the
coronavirus. This new evidence could provide guidance to public health
officials on how to contain the spread of the disease.
“This provides
evidence that extensive control measures including isolation, quarantine,
school closures, travel restrictions and cancellation of mass gatherings may be
warranted,” Meyers said. “Asymptomatic transmission definitely makes
containment more difficult.”
Meyers pointed
out that with hundreds of new cases emerging around the world every day, the
data may offer a different picture over time. Infection case reports are based
on people’s memories of where they went and whom they had contact with. If
health officials move quickly to isolate patients, that may also skew the data.
“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.”
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