Tam: Omicron infectious up to 10 days

OTTAWA – The latest evidence does not show that the Omicron variant is contagious for a shorter time than previous versions of the virus that causes COVID-19, said public health chief Dr. Theresa Tam 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 isolation periods early.

“This is a difficult decision that the provinces have to make,” Tam said.

Three weeks ago, the United States Centers for Disease Control said data on infectious periods supported reducing the isolation period to five days from 10 if people wore masks after leaving isolation.

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

In Canada, quarantine rules are set by provinces and territories, except in the case of international travelers. But the Canadian Public Health Agency still recommends people who are infected with COVID-19 isolate for at least 10 days after being tested positive or symptoms begin, whichever comes first.

All provinces and territories have stopped following that advice, beginning with Ontario and Saskatchewan on December 30th.

Nova Scotia, Prince Edward Island and Newfoundland and Labrador as well as the Yukon and Nunavut reduced the isolation period from 10 days to seven for vaccinated people. Every other province and the northwestern territories say five days.

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

Unvaccinated individuals still need to be isolated for 10 days everywhere, although in some places exceptions have been made for children who cannot yet be vaccinated.

Tam was asked by members of the health committee on Tuesday when Canada would change its guidelines, and she said the Canadian Public Health Agency is working to update its data on infectious periods.

“There is very little information,” she said. “But the studies we have managed to gather, including a recent one for Japan, suggest that the infection period is not shorter than the other variants because virus excretion and viral load only decrease on day 10 after symptom onset or sampling after diagnosis.”

The Japanese study is preliminary and still not peer reviewed, but it indicated that the amount of virus was highest among Omicron patients three to six days after the symptoms started and disappeared about 10 days.

It does not differ from previous variants, Tam said.

“A person who is infected, for example, is still able to excrete the virus and communicate this himself for up to 10 days,” Tam told lawmakers.

The Japanese study showed similar results as a data review in the UK published earlier this month.

However, that does not mean the isolation period cannot be adjusted with the right precautions, Tam said.

“We recognize that because so many people are infected with Omicron, it is currently extremely challenging to maintain business continuity and continuity in critical services,” she said.

Tam said reducing the isolation period involves “some risk” and makes other protective layers, such as masks, and testing even more important.

The United Kingdom reduced its isolation period from 10 days to seven before Christmas and further to five days on Monday. But the UK says the symptoms should be gone and the individual should have two negative quick tests taken on day five and day six.

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

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