OTTAWA -- Canada’s Chief Public Health Officer Dr. Theresa Tam says “active” discussions are underway with various countries, including the U.S., to permit the entry of Canadians with mixed COVID-19 vaccine doses.

Tam said the Public Health Agency of Canada (PHAC) has been presenting data to colleagues internationally on the effectiveness of a mixed-dose schedule, such as a dose of AstraZeneca followed by a dose of Moderna or Pfizer.

“Those [discussions] are progressing pretty well. But every country is trying to figure out right now the vaccine requirements, and the U.S. … is just beginning to pull together their policy,” she said, speaking to reporters during a COVID-19 briefing on Friday.

The U.S. Centers for Disease Control and Prevention website currently states that data on the safety and efficacy of a mixed-product series is limited, and that both doses of the series should be completed with the same product.

Canadians can still fly to the U.S., if they have proof of a negative molecular or antigen COVID-19 test taken no more than three days before their departure flight.

Countries like France and Germany have promoted mixing vaccines to elicit a stronger immune response in citizens.

However, while other European Union member states recognize Vaxzevria, the European-manufactured version of AstraZeneca, some have not authorized COVISHIELD, the Indian-made version of the same vaccine that has also been used in Canada.

The World Health Organization hasn’t issued formal guidelines on mixing and matching doses, instead advising that that information come from individual public health agencies.

Tam said PHAC is doing “everything we can” to facilitate recognition of Canadians’ varied vaccine programs, but that those hoping to travel abroad should check with their destination country about its specific vaccination policies.

In Canada, more than three million AstraZeneca shots have been administered, more than 43 million Pfizer shots have been administered, and nearly 18 million Moderna shots have been administered.

With files from CTV News’ Nicole Bogart.