It is probably safe and effective, but researchers are still gathering data to make sure.
The approved COVID-19 shots around the globe are all designed to stimulate your immune system to generate virus-fighting antibodies, although the way they do this varies, noted Dr. Kate O'Brien, director of the World Health Organization's vaccine unit.
"According to the basic principles of how vaccines work, we do believe the mix-and-match regimens will work," she said.
Researchers at Oxford University in the Uk are examining combinations of the two-dose COVID-19 vaccines produced by AstraZeneca, Moderna, Novavax and Pfizer-BioNTech. Smaller trials are also continuing in Spain and Germany.
"We really just have to get the signs in all them (vaccine) mixes," O'Brien said.
So far, limited data indicates an AstraZeneca shot followed by the Pfizer shot is safe and effective. The mix also appears to include a slightly higher likelihood of temporary side effects like aches and chills.
That is because mixing and matching different types of vaccines can frequently create a stronger immune response, stated Lawrence Young, a virologist at the University of Warwick in the United Kingdom.
In some places, health officials already suggest mixing in select circumstances.
After the AstraZeneca vaccine was linked to exceptionally rare blood clots, several European countries including Germany and France advocated people who obtained it as a first dose get a Pfizer or Moderna shot as a second dose rather. On Thursday, Canada made the same recommendation.
Some places like Britain say folks should aim to get exactly the same vaccine to get their second dose when at all possible. If they got AstraZeneca because their very first shot, they're advised to get another vaccine only if they have a history of blood clots or other conditions that might put them at higher risk of clots.