Mixing certain COVID-19 vaccines provides better immune response: British researchers

British researchers have found that patients who received a first Pfizer or AstraZeneca COVID-19 vaccine dose followed by a second Moderna shot developed an improved immune response. 

The research, published on Monday in The Lancet, determined that those who received a Moderna dose after an initial Pfizer or AstraZeneca shot experienced higher antibody and T-cell responses than patients who received the two doses of their original vaccine.

The results support a more flexible approach to the worldwide vaccination effort that doesn’t limit patients to only the type of dose from their initial vaccination, which could make vaccinating the global population easier.  

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Patients who received the first shot of AstraZeneca before a second Novavax dose also saw increased antibody and T-cell responses than those with two doses of the AstraZeneca vaccine. 

But Pfizer recipients who got their second shot with Novavax showed reduced antibody and T-cell responses compared to two-dose Pfizer recipients, although the responses were still higher than those with two AstraZeneca doses.

The research came from the University of Oxford-led Com-COV2 trial that involved 1,070 patients across nine sites backed by the National Institute for Health Research.

Matthew Snape, an associate professor in pediatrics and vaccinology at the university, said in a release that the mix-and-match method with vaccines that use different technologies, such as mRNA and protein-based vaccines, is a “relatively novel approach” to vaccinations.

“This will help get the world immunized against COVID-19 as quickly as possible,” Snape, who served as the chief investigator in the study, said. 

“This has implications beyond COVID-19 and will inform new approaches to immunization against other diseases that are, as yet, not vaccine preventable,” he added.

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Scientists expanded the trial to analyze the effects of mix-and-match for second doses among those aged 12-16 years old in September. 

The results come as many low- and middle-income countries are still desperate for vaccine doses, making vaccine administration and distribution much more difficult. Being able to mix second doses could allow these countries to move faster in boosting their population’s immunity as the delta and omicron variants wreak havoc worldwide.

The available vaccines in the U.S. include the Pfizer, Moderna and Johnson & Johnson doses, since the AstraZeneca and Novavax vaccines do not yet have emergency use authorization.

The U.S. Food and Drug Administration approved mix-and-match doses for booster shots in October after previously requiring patients to receive doses of the same vaccine they originally got. But currently, patients have to complete their initial vaccination before that, either with two doses of the same mRNA vaccine or one dose of Johnson & Johnson.