The CDC said last week it would accept any vaccine authorised for use by US regulators or the World Health Organisation.

"While CDC has not recommended mixing types of vaccine in a primary series, we recognise that this is increasingly common in other countries so should be accepted for the interpretation of vaccine records," a CDC spokeswoman said.

Representative Brian Higgins, a New York Democrat representing a district along the Canadian border, had on Friday asked the CDC if it would accept the mixed vaccine doses noting "nearly four million Canadians, equivalent to 10 per cent of their fully vaccinated population, have received mixed doses of the available mRNA COVID-19 vaccines - this includes the AstraZeneca vaccine."

The CDC said the vaccines approved by the Food and Drug Administration (FDA) for use, as well as those authorised by the WHO, will be accepted for entry into the United States, including the AstraZeneca vaccine.

The CDC said "individuals who have any combination of two doses of an FDA approved/authorised or WHO emergency use listed COVID-19 two-dose series are considered fully vaccinated".

The CDC plans to answer other questions and release a contact tracing order for international air visitors by October 25.

Meanwhile, the US will lift travel restrictions for fully-vaccinated international visitors from November 8, ending historic restrictions that had barred much of the world from entering the country for as long as 21 months.

The unprecedented travel restrictions kept millions of visitors out of the United States from China, Canada, Mexico, Australia, India, Brazil, much of Europe and elsewhere; shrunk US tourism and hurt border community economies. They prevented many loved ones and foreign workers from reuniting with families.

US allies had heavily lobbied the Biden administration to lift the rules. Many praised Friday's announcement, including Sweden's ambassador to the United States Karin Olofsdotter, who called it "very welcoming news".

Australian Associated Press