Coronavirus pandemic: Do travel bans help? Wuhan lockdown slowed down virus spread in China only by 3 to 5 days
In a bid to check the spread of COVID-19, many countries are imposing travel restrictions. But do they work? According to an analysis, travel bans imposed in Wuhan slowed down the spread of COVID-19 by only a few days within China. However, at the same time, it brought the world more time: 77% fewer cases were imported from China due to the Wuhan lockdown.
On January 23, 2020, China enacted a lockdown in Wuhan City to limit the spread of the COVID-19 outbreak. The lockdown was expanded to 15 other cities in Hubei province on January 24.
While the travel ban was imposed from January 23, researchers show that by then, COVID-19 had already spread to other cities within Mainland China. The travel quarantine around Wuhan only modestly delayed the virus spread to other areas of Mainland China, they say.
“Motivated by the rapid spread of COVID-19 in Mainland China, we use a global metapopulation disease transmission model to project the impact of travel limitations on the national and international spread of the epidemic. The model is calibrated based on internationally reported cases, and shows that at the start of the travel ban from Wuhan on January 23, 2020, most Chinese cities had already received many infected travelers,” say researchers in their findings published in Science.
“The travel quarantine of Wuhan delayed the overall epidemic progression by only 3 to 5 days in Mainland China, but has a more marked effect at the international scale, where case importations were reduced by nearly 80% until mid-February,” they say.
The researchers also found that even in the presence of strong travel restrictions, a large number of individuals exposed to COVID-19 have been traveling internationally without being detected.
The team warns that going forward, travel restrictions will only have a modest impact on the spread unless community transmission is stopped. Even with 90% travel bans, disease spread will not stop unless they are paired with public health interventions and behavioral changes. “Transmission-reduction interventions will provide the greatest benefit to mitigate the pandemic,” they add.
According to current estimates, over 5,800 have died and over 156,000 have fallen sick with the virus.
Travel bans won’t help if there’s community transmission
President Donald Trump's travel ban on 26 European nations has come into force in the US. The ban applies to non-Americans who have been in the Schengen border-free travel area within 14 days of traveling to the US. The ban has now been extended to the UK and Ireland starting at 04:00 GMT on Tuesday.
Many others have imposed similar travel restrictions. Italy has been on lockdown since March 9, when a national quarantine was announced. Cambodia is banning foreign nationals traveling from the US and virus-hit European countries for 30 days.
Turkey has stopped travel to and from nine European countries. The Czech Republic has shut its borders to travelers from 15 nations, including the UK.
Australia has imposed travel bans on foreign nationals from China, South Korea, Iran, and Italy. Japan has also banned entry to passengers who have been in affected regions of China, South Korea or Italy within the last 14 days.
However, according to health experts, such blanket travel restrictions on outsiders are not of much help once a disease has started circulating within a community.
Strict travel restrictions could delay the spread of disease, if not reduce the number of people who become infected, allowing hospitals and other healthcare facilities to be better prepared. However, say experts, the restrictions only work if used along with other robust measures to control the infection in the community. This includes containment, quick diagnosis, and isolation.
“Unfortunately, travel bans sound good. But we’re way past the point where simply restricting travel is a reasonable response,” Bill Hanage, an epidemiologist at Harvard’s TH Chan School of Public Health, told The Guardian.
Further, the US restrictions do not bar American citizens, permanent residents or their family members.
“An Italian who’s living in Italy, and a French person who’s living in Italy — and an American — could all be just as likely to carry the virus. The ban that Trump announced, it’s focused a little more on nationality and not exposure,” Danielle Ompad, an epidemiologist at New York University, told The Guardian.
The World Health Organization (WHO) has also maintained that travel restrictions should be very carefully considered. “They should be public-health-evidence-driven, they should be of short duration and they should never be carried out in the absence of a comprehensive set of measures to contain or control the disease,” says the WHO.
Imported cases picked up again post Wuhan ban
While the number of cases imported internationally initially shows a marked decrease, it picks up again in the following weeks with importation from locations in Mainland China.
“The model indicates that while the Wuhan travel ban was initially effective at reducing international case importations, the number of cases observed outside Mainland China will resume its growth after 2-3 weeks from cases that originated elsewhere,” say experts in the current study.
The model indicates that after the travel restrictions in Wuhan were implemented on January 23, the top 5 ranked cities as the origin of international case importations are Shanghai, Beijing, Shenzhen, Guangzhou, and Kunming.
“Before the travel ban, ≈86% of the internationally imported cases originated from Wuhan. After the travel ban, the top 10 contributors to the relative risk are needed to account for at least ≈80% of the internationally imported cases where the top three contributors are: Shanghai, (28.1%), Beijing (14%), and Shenzhen (12.8%),” says the team.
In terms of the relative risk of importation, the experts found that the countries at higher risk of importation after the implementation of the Wuhan travel ban are: Japan (11% pre-travel ban, 13.9% post-travel ban), Thailand (22.8% pre-travel ban, 13% post-travel ban), Republic of Korea (7.4% pre-travel ban, 11.3% post-travel ban), Taiwan (9.5% pre-travel ban, 10% post-travel ban), and USA (4.7% pre-travel ban, 5.7% post-travel ban).
Starting early February 2020, 59 airline companies suspended or limited flights to Mainland China and several other countries have also imposed government-issued travel restrictions, says the research team.
But sustained 90% travel restrictions to and from Mainland China only modestly affect the epidemic trajectory unless combined with a 50% or higher reduction of transmission in the community, says the analysis.
Rapid contact tracing is critical
To contain the global spread of COVID-19, border control measures, such as airport screening and travel restrictions, have been implemented in several countries.
Researchers of another related study found that 779 cases would have been exported by February 15 without any border or travel restrictions by China and that the travel lockdowns enforced by the Chinese government averted 70.5%. In addition, during the first three and a half weeks of implementation, the travel restrictions decreased the daily rate of exportation by 81.3%.
But the analysis shows that while measures such as travel bans and airport screening and the China travel lockdowns have likely slowed the rate of exportation from mainland China to other countries, they are insufficient to contain the global spread of COVID-19.
With most cases arriving during the asymptomatic incubation period, the results suggest that rapid contact tracing is essential both within the epicenter and at importation sites to limit human-to-human transmission outside China.
The researchers explain with early estimates suggesting a “presymptomatic incubation period” lasting up to two weeks, a large proportion of infected travelers may not be detected during screening, says the team. The study suggests that the first exportation event was likely to have occurred almost three weeks before the travel ban.
“Our results show that the daily risk of exporting at least a single SARS CoV-2 case from mainland China via international travel exceeded 95% on January 13, 2020,” say researchers in an analysis published in PNAS.
To curtail local outbreaks, it is important to identify imported cases in the incubation period before onward transmission occurs, they say. The experts argue that public health officials would have to identify and quarantine these imported cases within a week of arrival to limit the risk of transmission, with earlier detection of cases being more efficient.
“We find that airport screening has only a moderate benefit during the early stages of the epidemic, as about 64% of infected individuals travel during the incubation period and exhibit symptoms an average of 3 days after arrival,” says the team.