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"If you are six months post any vaccine and COVID illness, then you should get your bivalent vaccine, you should get that booster," Sharma said.

"And that'll help you in terms of serious illness protection, but it will also give you some protection, especially in the short term against potentially getting infected with COVID."

This shot was authorized through a process similar to the one used for annual flu shots, which meant the approval could come much quicker. Sharma said the vaccine has already been given to nearly five million Americans and no safety signals have arisen.

ºÃÉ«tvs can get the shot as early as three months after their most recent booster, but Sharma said she wouldn't recommend doing it sooner than that. She said doses too close together can limit the effectiveness of the extra dose.

Health Minister Jean-Yves Duclos said 2.8 million doses of the new Pfizer booster will be shipped to Canada next week, and 11 million by the end of the year. Provincial governments will announce separately who will become eligible to get this shot and when.

Given the slowing uptake of boosters in Canada, 11 million doses will likely be more than enough to give a booster to those who want one.

While 81 per cent of all ºÃÉ«tvs have the first two doses of a vaccine, only 49 per cent followed advice to get a third dose, and 13 per cent followed up with the recommendation to get a fourth dose.

Combination vaccines, referred to as bivalent by vaccine makers, target more than one strain of the virus. Pfizer's BA.4 and BA.5 boosters is the second bivalent authorized in Canada.

A Moderna booster approved five weeks ago targets the original virus and the first strain of the Omicron variant.

Sharma said there isn't a lot of difference between the results of being boosted with one or the other, even though BA.4 and BA.5 are the dominant strains in circulation now.

Health Canada data show in mid September, 88 per cent of COVID-19 cases that were sequenced to identify the strain proved to be BA.5 and nine per cent were BA.4.

The original vaccines authorized almost a year ago now were very good at preventing infection but Omicron threw a big wrench into that. While the vaccines remained excellent at preventing serious illness and hospitalization, they stopped being very good at preventing people from getting infected.

Sharma said it's not really clear yet how infection rates will be affected as the new booster rolls out because there are so many different strains circulating.

There are at least four different versions of both the BA.4 and BA.5 strain alone.

"I think it's really an interesting kind of place in the pandemic, where we haven't been before there's a bit of a variant soup out there," said Sharma.

"There is some evidence that at least some of the top candidates for the ones that might emerge in the next wave would be covered by these vaccines. But I think it's, you know, we're still learning as we go with the pandemic."

Dr. Howard Njoo, the deputy chief public health officer, said while the updated combination Omicron vaccines are good, people who recently got a booster using one of the original vaccines need not worry that they can't get an Omicron booster for another three to six months.

"Evidence continues to show that original mRNA vaccines provide good protection against serious illness and hospitalization," he said.

Canada's chief public health officer, Dr. Theresa Tam, said case numbers are starting to tick up again but there are signs the end of the pandemic is in sight.

ºÃÉ«tvs can help bring that end closer by continuing to do what they can to slow the spread, including getting booster shots.

Njoo acknowledged there has been vaccine fatigue over the past two years, but said he believes people will start to think about updating their COVID-19 vaccines in a similar way to the annual flu shot.

"We certainly anticipate that we will increase and improve uptake," he said.

This report by ºÃÉ«tvwas first published Oct. 7, 2022.