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Is it OK to mix and match COVID-19 vaccines? Oxford researchers begin trial.

A healthcare worker giving someone a vaccine.
(Image credit: Shutterstock)

Researchers at the University of Oxford in the U.K. will begin to test what happens when they give people a mix of different COVID-19 vaccines.

Amid a shortage of vaccine supplies and the threat of emerging coronavirus variants, such an approach might provide an answer for both, according to a statement. The study, which will include more than 800 volunteers across England who are 50 years of age or older, is the first to analyze a mix-and-match approach to COVID-19 vaccination.

Some participants will be given a first dose of the Oxford-AstraZeneca vaccine followed by a second dose of the same vaccine or the Pfizer vaccine; and some will be given the Pfizer vaccine followed by a second dose of the same vaccine or the Oxford-AstraZeneca vaccine.

Related: Quick guide: COVID-19 vaccines in use and how they work

Some participants will be given the two doses four weeks apart and others will be given the vaccines 12 weeks apart (which is in line with the U.K.'s policy to vaccinate as many people as possible and delay the second dose by 12 weeks). The participants will all periodically give blood samples and the researchers will test the impact of the mixing and matching on their immune responses and will also test for any adverse reactions. 

"Given the inevitable challenges of immunizing large numbers of the population against COVID-19 and potential global supply constraints, there are definite advantages to having data that could support a more flexible immunization program, if needed and if approved by the medicines regulator," Dr. Jonathan Van-Tam, the deputy chief medical officer and senior responsible officer for the study said in the statement. "It is also even possible that by combining vaccines, the immune response could be enhanced giving even higher antibody levels that last longer; unless this is evaluated in a clinical trial we just won’t know."

The Oxford-AstraZeneca and the Pfizer vaccines were developed using two different approaches; to spur the immune system, the former uses a weakened adenovirus to deliver the genes of the spike protein and the latter uses messenger RNA enveloped in a nanoparticle.

It's not yet clear if giving two very different vaccines would confer any benefit. The closest data we have to this is on Russia's Sputnik V vaccine, which was 91% effective in preventing COVID-19 and uses two slightly different versions of its vaccine for its two separate doses, according to the Associated Press. Still, both versions were developed using the same adenovirus-based technology.

If the study does indeed show that a mix-and-match approach confers great benefit, it will still be formally reviewed for safety and efficacy by the Medicines and Healthcare products Regulatory Agency (MHRA) before such an approach is taken to vaccinate the rest of the public.

Currently, guidelines in the U.K. and in the U.S. say that COVID-19 vaccines should not be used interchangeably unless the same type of vaccine isn't available for a person's second dose or if it's unknown what vaccine the person got as a first dose, according to the AP.

The mix-and-match trial is run by the U.K.'s National Immunization Schedule Evaluation Consortium with government funding and will last for 13 months.

Originally published on Live Science.

Yasemin Saplakoglu

Yasemin is a staff writer at Live Science, covering health, neuroscience and biology. Her work has appeared in Scientific American, Science and the San Jose Mercury News. She has a bachelor's degree in biomedical engineering from the University of Connecticut and a graduate certificate in science communication from the University of California, Santa Cruz.