Health Canada approved on Thursday the use of the Pfizer-BioNTech COVID-19 booster vaccine that targets the BA.4 and BA.5 strains of the Omicron variant.
The vaccine, which is approved for people at least 12 years old, can be given three to six months after a second dose of the primary vaccine series, or the most recent booster shot.
Health Canada said the bivalent booster has already been given to nearly five million people in the United States and there have been no new safety concerns.
"Canada will have enough supply of the Omicron-targeting bivalent vaccines to cover the anticipated demand for fall boosters," Dr. Howard Njoo, Canada's deputy chief public health officer, said on Thursday.
Njoo said people who already had a booster shot of the original mRNA vaccines do not need to get a bivalent booster.
"Evidence continues to show that original mRNA vaccines provide good protection against serious illness and hospitalization," he said.
It is the second combination vaccine greenlighted by Health Canada's vaccine review team, but the first that targets the virus strains that are now most common in Canada.
The Moderna combination shot approved five weeks ago targets the original virus and the first Omicron variant, while the Pfizer shot targets the BA.4 and BA.5 strains. The Moderna vaccine is approved for people who are 18 and older.
Health Canada said 88 per cent of the COVID-19 cases identified in mid-September were BA.5 and nine per cent were BA.4.
"We are starting to see an increase in cases, we are heading into the fall season, there's a lot of gatherings and festivals that are happening as well, so we know that there's going to be increasing circulating virus," said Dr. Supriya Sharma, Health Canada's chief medical adviser.
If it has been less than three months since a COVID-19 infection or a booster, the new bivalent vaccine is not recommended because it will not be as effective, Sharma said.
Health Canada was already reviewing a BA.1 vaccine from Pfizer, but said it chose to prioritize the newer vaccine because it was expected to be in higher demand.
Officials say at this stage of the pandemic it is challenging to know what variants may be emerging next, but that Omicron seems to have the most staying power.
"There's a bit of a variant soup out there right now," Sharma said.
Uptake of booster vaccines has not been anywhere near as high as the initial vaccines. About 82 per cent of Canadians received two doses of a vaccine as of Sept. 11, but just shy of 50 per cent have at least one booster.
"We have lots of experts behind the scenes looking at what different ways or what ways we can reinforce in terms of giving the right information, not just to the average Canadian to be quite honest, but also to health-care providers and community leaders using multiple platforms, so that people at the end of the day can make an informed decision," Njoo said.
He 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."