Latest research shows Omicron is infectious for up to 10 days: Tam

OTTAWA — The latest evidence does not show that the Omicron variant is contagious for less time than previous versions of the virus that causes COVID-19, public health official Dr. Theresa Tam said Tuesday.

But Tam told the House of Commons Health Committee that the large number of Omicron infections is stressing the workforce and is a reason to adjust our risk tolerance to end periods early. isolation.

“It’s a tough decision for the provinces to make,” Tam said.

Three weeks ago, the US Centers for Disease Control said infectious period data supported reducing the isolation period to five days from 10, if people wear masks after leaving isolation.

This was based on data that the CDC suggested Omicron was most infectious for about two days before symptoms started and for three days after.

In Canada, quarantine rules are established by the provinces and territories, except for international travellers. But the Public Health Agency of Canada still recommends people infected with the COVID-19 isolate for at least 10 days after they test positive or the onset of symptoms, whichever comes first.

All provinces and territories have stopped following this advice, starting with Ontario and Saskatchewan on December 30.

Nova Scotia, Prince Edward Island and Newfoundland and Labrador, as well as Yukon and Nunavut, have reduced the isolation period from 10 days to seven days for those vaccinated. All other provinces and the Northwest Territories say five days.

Unlike the CDC, however, in Canada the shorter isolation period only applies to people who are fully vaccinated – and in the Northwest Territories to people who have received a booster shot.

Unvaccinated people are still expected to self-isolate for 10 days everywhere, although exceptions are made in some places for children who cannot yet be vaccinated.

Health committee MPs asked Tam on Tuesday when Canada would change its guidelines and she said the Public Health Agency of Canada was working to update its data on infectious periods.

“There is very little information,” she said. “But the studies we have managed to amass, including a recent one for Japan, suggest that the period of infectiousness is not shorter than the other variants, because viral shedding and viral load only really decrease at day 10 of onset of symptoms or specimen collection after diagnosis.

The Japanese study is preliminary and has yet to be peer-reviewed, but it indicated that viral load was highest in Omicron patients three to six days after symptoms started and disappeared around 10 days.

That doesn’t make it any different from previous variants, Tam said.

“An infected individual, for example, is still able to shed the virus and communicate it even for up to 10 days,” Tam told MPs.

The Japanese study showed similar results to a review of UK data published earlier this month.

However, that doesn’t mean the isolation period can’t be adjusted with the right precautions, Tam said.

“We recognize that with so many people infected with Omicron, it is currently extremely difficult to maintain business continuity and the continuity of critical services,” she said.

Tam said reducing the isolation period carries “some risk” and makes other layers of protection, like masks, and testing even more important.

The UK reduced its isolation period from 10 days to seven days before Christmas and then to five days on Monday. But the UK says the symptoms must be gone and the individual must take two negative rapid tests on the fifth and sixth day.

This report from The Canadian Press was first published on January 18, 2022.


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