OTTAWA (AP) — Canada’s chief public health officer is warning of a possible COVID-19 resurgence in the fall and winter.

Theresa Tam said Thursday the circulating omicron subvariants BA.4 and BA.5 are even more transmissible and able to evade immunity than previous versions, making a rise in cases likely in coming weeks.

Tam and federal Health Minister Jean-Yves Duclos stressed the importance of up-to-date vaccination status, noting 40% of Canadians still have not received a booster following their primary two shots, putting Canada behind other G7 countries when it comes to three doses.

"As cases go up... in some areas of Canada, getting that booster, if you haven’t had it, now would be quite important, in particular going into the fall,″ Tam said.

The National Advisory Committee on Immunization has advised jurisdictions to prepare to offer another round of shots to people at increased risk of severe COVID-19 illness, regardless of the number of booster doses they’ve already received.

Tam said new vaccines tailored to omicron are in development but have not yet been evaluated by Canada’s drug regulator. She said officials are still waiting for data on what new protection the so-called bivalent vaccines could offer.