TORONTO/OTTAWA -- The U.S. says it will allow Canadians into the country who have received a mixed COVID-19 vaccine schedule, when the U.S. opens its borders to fully vaccinated travellers on Nov. 8.

The U.S. Centers for Disease Control and Prevention (CDC) says that although it has not recommended mixing doses for Americans, “we recognize that this is increasingly common in other countries so should be accepted for the interpretation of vaccine records."

Canada and some other countries have allowed the mixing of viral vector vaccines like AstraZeneca with the Pfizer and Moderna mRNA vaccines, while the U.S. has not.

With nearly four million Canadians having received a mixed vaccine schedule -- including Prime Minister Justin Trudeau -- the question of whether other countries would recognize their status as fully vaccinated has been an ongoing concern, particularly as borders begin reopening to fully vaccinated travellers.

Travellers are considered fully vaccinated if they have had both doses of a two-dose vaccine or one dose of a single-dose regimen at least two weeks before the travel date.

The announcement by the CDC is the latest in a series of developments this week that marks the beginning of the end of the closures along the world’s longest undefended border that has lasted a record 19 months. U.S. and Canada closed its land borders to all non-essential travel on March 21, 2020, 10 days after the World Health Organization (WHO) declared a pandemic.

Earlier this week, the CDC said it would recognize air travellers who had been fully vaccinated with any vaccine approved or recognized for emergency use by the WHO or the U.S. Food and Drug Administration (FDA). This would include AstraZeneca’s COVID-19 vaccine, even though it has not yet been approved for use in the U.S. Friday’s update made clear that the same policy would apply for those travelling to the U.S. by land.

The CDC updated its public health recommendations for fully vaccinated individuals on Friday, and said that “for the purposes of interpretation of vaccination records” individuals were considered fully vaccinated two weeks after receiving the last dose of an FDA or WHO approved or authorized vaccine, “or any combination of two doses of an FDA approved/authorized or WHO emergency use listed COVID-19 two-dose series.” While the recommended interval between the first and second doses vary, the CDC added that it would recognize any regimen where the second dose was “received no earlier than 17 days (21 days with a four day grace period) after the first dose.”

While Canada will still require any eligible American traveller entering the country to show a negative test result at the border, Canadian citizens will not be required to show proof of a negative test before crossing into the U.S. via a land or sea port of entry. U.S. air travel rules still require proof of a negative COVID-19 test taken no more than three days before departure.