Imposing travel restrictions alone has ‘modest’ effect on virus spread

March 07, 2020 08:50 pm | Updated 08:51 pm IST

Travel restrictions in areas that have been affected by novel coronavirus can only modestly reduce the spread of the outbreak, a new modelling study published in Science finds.

The spread of the virus can be reduced by cutting the transmission chain. This can be achieved through early detection and isolation of people found infected with the virus as well as by bringing about behavioural changes and raising awareness level in the community.

Even “sustained” restrictions on travel to and from mainland China by as much as 90% only can only “modestly affect the epidemic trajectory” unless combined with a 50% or higher cut in transmission in the community, the study found.

Shutting down Wuhan and imposing travel ban in the city on January 23 delayed the epidemic from spreading to other parts of mainland China by just three to five days.

Even when travel restrictions are as high as 90%, the epidemic in mainland China is delayed for no more than two weeks if concomitant steps to reduce virus transmissibility are not taken, the authors found.

One of the reasons is that by January 23 when travel ban was introduced in Wuhan, the virus had already spread to other parts of mainland China.

Travel restrictions to China introduced by several countries, including the U.S., and a reduction or suspension of flight to China by 59 airline companies have not achieved extraordinary results in reducing the spread of the virus outside China, the study finds.

There was an initial 10-fold reduction in the number of imported cases when travel restrictions from China were introduced. But according to the model, by March 1, the number of imported cases per day shot up to 170 and 35 for 40% and 90% travel restrictions, respectively.

The number of cases outside mainland China will “resume its growth” after two-three weeks from cases that had their origin elsewhere, the model suggests.

The reason: despite the travel restrictions to and from mainland China, a large number of people who were already infected by the virus have been travelling across national borders without being detected.

Of the several imported cases, a couple of cases could be “seeding multiple outbreaks” across the world, thus leading to an expansion of the epidemic. This was observed in the case of Iran, South Korea and Italy after mid-February.

“The concurrent presence of both travel and transmissibility reductions, however, produce a much larger synergistic effect visible by both delaying the epidemic activity in Mainland China and the number of internationally imported cases,” the authors write.

“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,” they note.

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