We’ve heard that COVID-19 vaccines are not mixed and matched and that both doses are needed from the same vaccine.
But a study is underway in the United Kingdom to see if that might be possible or even preferable.
The reason vaccines are not mixed and matched is because they were not studied that way. So we are unsure if they would still produce the same high efficacy and safety.
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But there are good reasons to find out if they could be used interchangeably for the initial two doses and even for boosters down the road.
Oxford University researchers are conducting the clinical trial that began by looking at the immune responses of trial participants given first the AstraZeneca vaccine and then the Pfizer shot, or the other way around.
The trial is now expanding to include the Moderna and Novavax vaccines too. If it was possible, mixing and matching could help ease vaccine supply shortages and speed up vaccination programs.
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“Vaccine supply may not be as regular. You may get a big delivery of one vaccine and then a few months later a big delivery of another vaccine,” Professor Matthew Snape, researcher at University of Oxford. “You’re not going to be able to control the supply in the first and second doses as well, perhaps as some other countries. So these mixed schedules might well be the key to getting two doses into as many people in the world as possible.”
Researchers said there have been hints in studies done in mice that combinations of vaccines might actually produce a better overall immune response. However, that needs to be studied in humans.
Mixing and matching is happening now in some part of the world by necessity. The AstraZeneca vaccine has been stopped in France for people under age 55 after reports of rare blood clots. Those who already received a first dose of AstraZeneca will be offered a different vaccine for their second dose.
The U.K. trial will test multiple combinations of available vaccines. Results of the study could be available by the summer.