Montreal·CBC Explains

What the science says on travel bans, as experts warily eye new COVID-19 variants

Does sealing borders work to prevent the spread of COVID-19? Based on the available scientific evidence, the short answer is: yes, it can, though that comes with some caveats.

Some people, including the Quebec premier, want the prime minister to ban all non-essential flights

A passenger makes her way through Montreal's Pierre Elliott Trudeau Airport earlier this month. Some, including Quebec Premier François Legault, want the prime minister to ban non-essential foreign flights. (The Canadian Press)

Prime Minister Justin Trudeau has advice if you're making travel plans for spring break: ditch them, now.

Some, including Quebec Premier François Legault, want the prime minister to go a step further and ban non-essential foreign flights altogether.

The merits of travel bans are once again being debated widely. Much of that has to do with epidemiologists who are fretful about highly contagious COVID-19 variants from the United Kingdom, South Africa and Brazil.

But does sealing borders work to prevent the spread of COVID-19? Based on the available scientific evidence, the short answer is: yes, it can, though it has a lot to do with timing.

Here's a look at some of the main questions in the Quebec debate over travel bans.

Are flights returning from holiday destinations driving viral spread in Quebec?

No. The novel coronavirus arrived here in early 2020 because of international travel — as one might intuit — but the main problem now is community spread. Contagious carriers are infecting their friends, family, schoolmates or work colleagues.

According to Dr. Mylène Drouin, the director of public health for the Montreal region, "we have [current] cases that are imported from travellers, but it is not an important proportion of new cases."

One major study in 2020 found international travel is likely responsible for between one and 10 per cent of active cases in any given country. An interim report from a study conducted at Toronto's airport last fall detected coronavirus in one per cent of travellers arriving from abroad.

Incoming travel is an issue, but nowhere near the most pressing one.

Passengers in the international arrivals hall at Montreal's Trudeau Airport on Dec. 29. An international panel found that implementing travel restrictions early in an epidemic did reduce transmission, though it was short-lived. (Graham Hughes/The Canadian Press)

What does the science say about whether travel bans are effective?

An international panel of researchers led by Dr. Karen Grépin, a Canadian-born public health professor at the University of Hong Kong, conducted a detailed review of the various travel restrictions employed around the world last year.

The panel found that implementing travel restrictions early in an epidemic did reduce transmission, but the researchers also concluded that "the effectiveness of these measures was short-lived," adding the caveat that the overall body of evidence remains thin.

As Dr. Kelley Lee, a Canada Research Chair at Simon Fraser University's faculty of health sciences and a co-author of the study, put it, "timing matters a lot; geography also matters a lot."

A mathematical model published in the Lancet last month also found travel restrictions are only likely to be effective in certain circumstances.

According to the model, travel restrictions will help reduce transmission in countries where there are few cases of COVID-19 and a lot of people arriving from abroad. Restrictions will also help in places "where epidemics are close to tipping points for exponential growth."

In that case, why shut down airports at this point?

Mainly because of variants of COVID-19 that are thought to be more contagious than earlier versions of the virus.

The key phrase in the Lancet paper is "close to tipping points for exponential growth." If the alarming infection curves in England and Ireland are any indication, Quebec may be closer to that point than anyone realizes.

"What worries us a lot about travellers is these new variants," Quebec's health minister, Christian Dubé, said Thursday. 

Tighter travel restrictions, said Lee, are perhaps best thought of as an extension of social distancing. It's not about keeping the new, more infectious variants of the disease entirely at bay. It's about slowing down their proliferation and buying time for the health-care system to absorb new patients.

"The main thing is: we have to stop spreading this virus around. The way you do that is by stopping people from moving around," said Lee.

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What about the land and sea borders?

Flights are only a small part of the problem, according to COVID Strategic Choices, a coalition of more than 100 health-care experts and workers.

Even with the current border restrictions, as many as 300,000 truckers and 50,000 essential workers cross the Canada-U.S. border each day.

The group is calling for the establishment of a "Canadian Shield," a near-zero COVID approach that includes strict travel restrictions, vaccination and screening for workers who do cross the border, closely monitored quarantines and more robust genomic testing for variants.

"There is a brief window to prevent what is happening in the U.K.," the group said in a petition, unveiled earlier this month, which urges the federal government to undertake swift action.

The way forward, the petition says, is to stop all but absolutely essential travel.

Transport trucks approach the Canada-U.S. border crossing in Windsor, Ont. Between 200,000 and 300,000 trucks travel between the two countries on any given day, despite travel restrictions. (Rob Gurdebeke/The Canadian Press)

How does one define 'essential' travel?

That's an important question. Canada has already closed its border to "non-essential" foreign travellers, and since November has imposed a mandatory quarantine that is monitored remotely.

But Ottawa has cited constitutional considerations that prevent it from banning Canadians from travelling abroad.

In any case, "essential" is a slippery concept. Quebec has had well-documented issues with defining it in terms of economic activity, and the goal-posts have shifted as the epidemiology has evolved.

Lee said the best way to define essential is to build on what other jurisdictions have done.

Here's Australia's definition: "The Australian Government has banned overseas travel, unless necessary for business, aid assistance or compassionate reasons."

Compare and contrast with the U.S., where the definition includes and is not limited to: all American nationals returning to the country, people travelling for school, work or medical reasons, and "individuals engaged in lawful cross-border trade." 

Experts like Lee would prefer Canada hew to the most restrictive definition possible, bolstered by more vigilant quarantine monitoring. That's the approach the research indicates can have the greatest impact.

Sisters Stephanie Frizzell, left, of Magog, Que., and Sherie Frizzell, right, of Newport Center, Vt., chat as they sit in lawn chairs last month at the U.S.-Canadian border between Stanstead, Que., and Derby Line, Vt. (AP)

What about inter-provincial and intra-provincial travel?

In an ideal world, that would stop too. Or at least be reduced to a faint trickle.

"The problem when people talk about travel restrictions is it's often in terms of what happens at the border. It's not just that; it has to be more," said Lee.

It's still possible to find Ontarians and Quebecers on the slopes in Whistler, she said. That shouldn't happen. Nor should non-essential travel between regions of the same province.

As it stands, the Quebec government isn't banning inter-regional travel, simply recommending against it.

"The capacity to control people's movements is limited, of course. The point is to reduce the number," Lee said, adding that smaller numbers are more easily tested and their contacts traced.

Even if one assumes it's not legally possible to stop people from travelling altogether, governments are certainly able to make it more difficult and more expensive.

Given the threat posed by new variants of the virus, Lee said, every little bit helps.

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