EDMONTON -- Alberta's top doctor on Thursday reported 1,429 COVID-19 cases, including the highest single-day count of variants of concern infections.

Forty-five per cent of Alberta's 12,187 COVID-19 cases are variant infections after the province added another 717.

Alberta has reported a total of 8,278 variant infections to date, and all but 49 are of the B.1.1.7 strain.

"We have now reached the point that if you test positive, you should assume that you have the U.K. variant," Dr. Deena Hinshaw said Thursday afternoon.

She said all three variants are more infectious than the original COVID-19 strain, with B.1.1.7 seeming to be 50 per cent more transmissible and P.1, first identified in Brazil, 100 per cent more contagious.

B.1.1.7 also seems to be more severe, Hinshaw said, while it's still unclear if the other two are.

However, Hinshaw added all three vaccines — Pfizer, Moderna and AstraZeneca — are effective at stopping the variant that is most common in Alberta.

On the other hand: "Vaccines seem to have a somewhat lower effectiveness against infection with B.1.351 variant, although they may still provide protection against severe outcomes."

P.1 vaccine evidence is mixed and it isn't clear if there will be an impact to effectiveness, Hinshaw said.

Alberta also reported 340 hospitalizations, including 83 people in ICU, and three deaths.

The province had administered nearly 756,000 vaccine doses as of Tuesday.