till allowing international travel at the end of January — its international proliferation was inevitable, the researchers concluded.
The paper added that travel restrictions alone only have modest impacts — other public health interventions, like increasing awareness, isolating sick people, and washing hands frequently, are also necessary to slow the virus' spread.
A timeline of travel restrictions and coronavirus spread
The Chinese government announced that a contagious new virus was causing a pneumonia-like illness among Wuhan residents on December 31. However, some reports suggest people started getting sick in early December, so the researchers assumed in their models that 40 people in Wuhan got sick in early December.
Chinese authorities enacted travel restrictions on January 23: They closed the Wuhan airport, shut down bus and train service, and banned private cars on the roads except for necessary services.
Using a global disease-transmission model called "GLEAM," the researchers estimated that on January 22, the day before the travel restrictions went into effect, there were likely already 117,584 coronavirus cases in Wuhan and 7,474 cases in the rest of China.
That's far higher than the numbers reported at the time: On January 23, the World Health Organization had reported 375 cases in the Hubei Province, where Wuhan is located, and 196 cases in the rest of China. (There were also 10 cases internationally, all of whom had travel ties to Wuhan.)
"As of January 23, the epidemic was seeded in several locations across mainland China," the researchers wrote.
Given those estimates, the researchers found, the travel restrictions did not have any effect on the coronavirus' spread in Wuhan itself. Outside of Wuhan, their model suggests, the quarantine reduced the number of cases around mainland China by 10% by January 31 compared to projections of case totals without any travel restrictions. Still, by February 1, every province in China had reported at least one case.
China's quarantine bought the rest of the world time
The researchers found that the worldwide coronavirus case total would have spiked more quickly if travel from the city had had continued unchanged. The restrictions likely delayed significant international spread for about two to three weeks.
However, infected travelers were still flying internationally from other airports in China, since many airlines didn't stop flights until early February. The researchers estimated that there were 101 incidents in which infected travelers from other parts of China visited international destinations and spread the virus.
This tracks with the observed increases in cases in Japan and South Korea in mid- and late-February.
Public-health measures should be paired with travel restrictions
The researchers also found that unless travel restrictions are paired with public-health interventions and behavioral changes that reduce the risk of transmitting the virus, the bans alone are insufficient. The most effective way to slow or halt an infectious-disease epidemic is to reduce transmissibility, they said. This is done via the standard ways to lower the risk of germ spread: washing your hands frequently, avoiding touching your face, and staying away from those who are sick. Educating travelers and the public about the virus helps, too.
"Moving forward, we expect that travel restrictions to COVID-19 affected areas will have modest effects, and that transmission-reduction interventions will provide the greatest benefit to mitigate the epidemic," the researchers wrote.
In addition, urging people to self-isolate after potential exposure — staying home and avoiding contact with others — for 14 days will help prevent the disease from spreading. If you do have symptoms, wear a mask to stop germs from your mouth and nose from spreading.
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