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Model shows how many COVID-19 infected travellers could arrive at U.S. border in Ontario

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As the United States continues to grapple with an influx of new cases of the novel coronavirus, many are questioning when the Canada-U.S. border could potentially reopen to non-essential travel.

In a series of tweets on Friday, Ashleigh Tuite, an epidemiologist at the University of Toronto, provided an illustration of how many COVID-19 infected travellers could arrive at the Canada-U.S. border in Ontario, depending on the rates of infection in the U.S. and how many travellers are crossing overall.

The model offers insight into how far the coronavirus case count in the U.S. would need to drop in order to safely reopen the border.

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In the tweets, Tuite said currently the number of people crossing the Canada-U.S. border into Ontario is low, probably fewer than 1,000 to 5,000 a day.

Americans waiting for COVID-19 test told to be patient
Americans waiting for COVID-19 test told to be patient

On Saturday the U.S. Centers for Disease Control reported 74,818 new cases of COVID-19.

Tuite said if Ontario sees a thousand travellers a day at the U.S. border, approximately two of those people will be infected with COVID-19.

“And then if you increase that to 10,000 travellers every day we expect, on average, 17 people arriving that were infected with COVID,” Tuite told Global News.

Read more: Canada, U.S. extend border closure agreement until Aug. 21

She said about one-third of those cases would be symptomatic when they arrive at the border.

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“So those ones you would potentially identify just by a border screening and asking people to identify that they had symptoms,” she said.

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The other two-thirds of cases would either be in the incubation period or would be presymptomatic or asymptomatic.

“And for those cases, the biggest control that we have is quarantine,” Tuite explained.

Currently, anyone entering Canada must comply with a mandatory 14-day quarantine period.

Those who arrive in the country who are unable to prove they have a viable isolation plan will be taken by officials from the Public Health Agency of Canada to a facility to do so.

Should Canadians be concerned with surging COVID-19 cases south of the border?
Should Canadians be concerned with surging COVID-19 cases south of the border?

Tuite said if people are adhering to the rules, then the infected travellers “shouldn’t be an issue.”

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“The challenge is that if they’re not in compliance with those quarantine measures, then any of those cases could potentially spark a small outbreak,” she explained.

In the series of tweets, Tuite wrote that once the case burden in the U.S. declines to between 1,000 to 10,000 infections per day, Canada can ease border restrictions while keeping the imported case numbers low.

But, she said it’s “really hard to predict” when that could be.

Tuite said in April and May it seemed as though things might be under control in the U.S., but that the country is seeing a spike in new cases again.

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“So I don’t think you can really put a timeline on it,” she said.

For now, Tuite said she thinks it is safest that the border remains closed to non-essential travellers.

“This [model] is looking at the number of cases reported each day,” she said. “Multiply that over the course of a month and you’re talking about a lot of potential cases arriving,” she said.

“And even with good adherence to quarantine and screening, you only need one or two of those cases to not comply, to potentially be associated with a super spreader event and really set off a much larger outbreak,” she continued.

Should Canadians be travelling?

In a previous interview with Global News, Colin Furness, an infection control epidemiologist and associate professor at the University of Toronto, said travel needs to be kept to a minimum as much as possible with no exceptions for any kind of tourism.

He said beyond just keeping the border closed to Americans, Canadians should not be coming and going as they please.

“We shouldn’t be having that,” he said. “It’s not just about keeping Americans out if we want to make things better,” he said.

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“Canadians should not be leaving the country for tourism or business travel.”

U.S. cases spike

The United States remained the epicentre of the virus on Sunday.

According to a tally from Johns Hopkins University, by 12 p.m. ET Sunday, there were more than 4.1 million confirmed cases of COVID-19 in the country.

So far the virus has claimed 146,484 lives in the U.S.
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The federal government announced the country’s border with the U.S. would be closed to all non-essential travel in March.
Last week, the two countries agreed to keep their shared borders closed to non-essential traffic until at least Aug. 21.

Read more: Majority of Canadians polled want U.S. border closed until end of 2020: Ipsos

And it appears an overwhelming majority of Canadians support the decision.A poll conducted by Ipsos exclusively for Global News earlier this month found that 85 per cent of Canadians said they want to keep the Canada-U.S. border closed until at least the end of 2020.The survey also suggested that anxiety surrounding travel is high.Ninety-three per cent of the poll’s respondents said they felt it would be “too risky” to travel to the U.S. this summer.–With files from Global News reporters Olivia Bowden and Maryam Shah
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