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Trial looking at mixing-and-matching different COVID vaccines could be game-changer

U.K. trial tests mixing vaccines over 2 shots
U.K. trial tests benefits of giving different COVID-19 vaccines for first, second shots 03:11

Oxford, England — While most COVID-19 vaccine trial volunteers have no idea whether they're getting the real vaccine or a placebo, for the volunteers participating in a potentially paradigm-shifting new study in the U.K., there is no placebo. It's not a question of whether they've had a shot, but which one — or rather, which two. 

As CBS News correspondent Charlie D'Agata reports, it's the first COVID-19 vaccine trial of its kind, and scientists say the results could revolutionize the future of vaccine distribution while also offering the most powerful weapon yet against emerging coronavirus variants.

D'Agata met Reeka Trikha right as she was about to get her first injection as part of the trial. She had no idea what was about to be shot into her arm.

"I'll leave it in the capable hands of the doctors," she said as she took the leap of faith.

The scientists behind the Oxford University-led trial are very deliberately mixing things up — testing not just one vaccine but combining doses of two different drugs to see what happens.

More than 800 volunteers aged 50 and above are taking part in the trial. Some are given a Pfizer "prime" shot followed by an AstraZeneca booster, a second group gets AstraZeneca followed by Pfizer, and a third set of participants gets the same vaccine twice — the standard way — for comparison.  

Shots are being administered at both four and twelve-week gaps in different trial groups to see what works best.

U.S. study finds AstraZeneca COVID vaccine 79% effective 02:40

"With that knowledge, we can have complete confidence that a number of different vaccines can be rolled out and implemented in a population very quickly, very efficiently, without any concern about inadvertent mixing of the combination," Professor Paul Heath, Director of the Vaccine Institute at St. George's University of London and the principal investigator at one of the eight trial sites across the U.K., told CBS News.

Evidence from the trial could suggest that not only the Pfizer and AstraZeneca vaccines, but potentially any combination of any COVID-19 vaccines could be safe, and effective at preventing symptomatic infections. That flexibility could go a long way toward easing the inevitable supply issues that are already popping up around the globe.

But it could be even better news than that: Heath says that using alternating vaccines between an individual's two doses could actually produce better overall protection against emerging variants of the virus.

"Potentially with a prime boost of different vaccines, the broader response, the broader immune response that ensues will be sufficient to deal with, for example, the South African variant," he said, referring to a strain of the virus that has shown some degree of resistance to the current vaccines on offer.

As unpredictable as the virus has been, two challenges ahead are certain: Global shortages will get worse, and the virus will continue to mutate.

The results of the trial in Britain may offer the best hope to address both of those problems.

For those who've already had a vaccine, it remains unclear exactly how long the protection will last. If we do all end up needing booster shots, the Oxford research will shed light on whether we may be better off switching up the vaccine the next time around.

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