Alberta finds 1.5% of international travellers reporting no symptoms actually had COVID-19

Alberta Premier Jason Kenney recently described his government's pilot program aimed at shortening the quarantine time of international travellers as a "success," noting only 1.48 per cent of roughly 20,000 people arriving in the province tested positive for COVID-19 upon arrival.

"This compares to an overall positivity rate in the province of around seven per cent," Kenney said during a New Year's Day press conference, in which he defended the recent overseas travel of members of his own government.

That isn't comparing apples to apples, however.

Alberta's overall positivity rate, indeed, averages around seven per cent, but that's among a group of test subjects who have COVID-19 symptoms or have been in close contact with a known case.

The pilot program, by contrast, specifically excludes these types of people. To participate, travellers must declare that they have no symptoms and no known exposures.

That means comparing the two figures is "absolutely apples to oranges," said Dr. Craig Jenne, an associate professor of microbiology, immunology and infectious diseases at the University of Calgary.

It means we are, for every international flight, importing potentially three or four infected people.- Dr. Craig Jenne

Rather than being reassured, Jenne said he was a bit taken aback when he heard 1.5 per cent of non-symptomatic travellers were testing positive.

"As a number it seems low, but when we look at it in context … I thought it was actually quite high," he said, noting international flights can carry hundreds of passengers.

"It means we are, for every international flight, importing potentially three or four infected people."

And he said the stakes of international travel have been raised with new, more transmissible strains of the virus circulating overseas.

Variant 1st detected in South Africa now in Alberta

On Friday, Alberta Health reported Canada's first case of a new variant that originated in South Africa.

This particular variant is believed to be more infectious than the original coronavirus that causes COVID-19. It quickly became dominant in South Africa's coastal areas.

Some researchers in the United Kingdom have also expressed concerns about the effectiveness of current vaccines against this variant, but say more study is needed.

Meanwhile, another variant that originated in the U.K., known as B117, has been linked to a sharp and sudden resurgence of the disease in that country. In light of the rapid spread of this strain, Britain entered a third national lockdown last week.

The B117 variant first appeared in Canada in late December, when it was detected in two people in Ontario who had been in contact with a traveller who had recently returned from the U.K.

Already, the spread of B117 in Ontario is alarming public health officials, with worst-case-scenario modelling suggesting it could become the dominant strain in that province by late February.

On Sunday, Japan announced a new coronavirus variant had been detected in four travellers arriving from Brazil. Studies are underway to determine how it responds to existing vaccines.

The Public Health Agency of Canada "has been working with provinces, territories and international partners to enhance monitoring for the presence of any virus variants in Canada," according to Chief Public Health Officer Dr. Theresa Tam.

Tam said Saturday that 14 cases of the B117 strain had been detected in Canada, in addition to the one case in Alberta of the variant that originated in South Africa.

That case involved a recent traveller who is now in quarantine. Alberta Chief Medical Officer of Health Dr. Deena Hinshaw said there was no evidence the variant had spread to anyone else in the province.

Measures to contain imported virus

Travellers arriving from the U.K. or South Africa are not eligible to participate in Alberta's pilot program and must quarantine for the full 14 days required of non-participants.

Travellers arriving from other destinations who do participate in the program must take a COVID-19 test upon arrival and remain in isolation for up to 48 hours, until they receive their result.

Those who receive a negative result can leave quarantine on the condition they do daily check-ins with public-health officials and take a second COVID-19 test on the sixth or seventh day after their arrival.

The 1.5 per cent of travellers who tested positive on their first test "never leave quarantine," said Alberta Health spokesperson Tom McMillan. They must continue to isolate and follow all other mandatory restrictions.

Alberta Health couldn't say what proportion of travellers participate in the program. Data on travellers' compliance with the public-health rules also wasn't available.

And what about that 1.5-per-cent figure? Is that positivity rate high, low or about what we should expect?

Comparable data on that was not available, either.

Past, non-symptomatic data not a good comparison

Last summer, Alberta did non-symptomatic testing of the general population, so one might think that would offer a better point of comparison.

From June to September, roughly 659,000 tests were performed on Albertans who reported having no symptoms and, last fall, the province said only 0.11 per cent of those tests came back positive.

But McMillan said you can't directly compare that figure with the 1.5-per-cent positivity rate among non-symptomatic travellers.

A key difference, he said, is the fact that the 0.11-per-cent figure from last fall did not include people who later showed symptoms.

That is believed to be a common occurrence among the 1.5 per cent of travellers who tested positive, despite reporting no symptoms at their time of arrival. Since the virus has a long incubation period, people can be carrying the virus for several days prior to feeling ill.

Jenne, the infectious-disease professor, said it's possible some travellers participating in the program may have lied about having no symptoms, but he doesn't believe it would be a large number.

Rather, he said, it's more likely that many of them were infected and simply didn't know it yet because they were in "that two-to-three-day window" before symptoms start to show up.

That said, he's still concerned that 1.5 per cent of travellers were found to be positive for COVID-19.

"Although the actual case numbers may be small compared to the provincial case numbers, every one of those people who is coming into the province that is infected has the potential of importing a new strain, which could spread more easily, cause more severe disease or risk things such as vaccine protection," Jenne said.

"So we really want to avoid importing new variants of the virus, and we're seeing more and more of those around the world right now."