Study suggests mixing vaccines provides greater protection against COVID-19

(NEXSTAR) – A prominent study from the UK looking at the effects of mixing COVID-19 vaccines found that participants saw a better immune response when they received a different second dose weeks after their first.

The findings from the University of Oxford-led Com-Cov study, headed by Professor Matthew Snape, are encouraging for countries where vaccine supply may be more limited.

“What we’re seeing is that there’s a great amount of flexibility in the primary immunization schedule,” Snape told The Guardian. “Just because you’ve received dose one of a particular vaccine, doesn’t mean you have to receive the same vaccine for dose two.”

The study also showed that mixing was safe, with no issues found among the 1,070 participants who ranged in age from 50 years to 78 years of age. Researchers looked at a variety of combinations of Oxford-AstraZeneca, Pfizer, Novavax and Moderna vaccines.

“I think the data from this study will be especially interesting and valuable to low- and middle-income countries where they’re still rolling out the first two doses of vaccines,” Snape told Reuters. “We’re showing … you don’t have to stick rigidly to receiving the same vaccine for a second dose … and that if the program will be delivered more quickly by using multiple vaccines, then it is OK to do so.”

The researchers found that getting a first shot of the Pfizer vaccine and following it up with a shot of Moderna 8–12 weeks later was better than getting two shots of Pfizer.

People who took the AstraZeneca-Oxford vaccine for both shots saw lower levels of antibodies and T-cell responses than those who took AstraZeneca for the first and Moderna or Novavax for the second, according to the study.

The Pfizer/Moderna combo, both created with mRNA technology, produced the greatest antibody response, according to the Lancet. Data suggested that adenovirus- and protein-based vaccines, such as Novavax, might be linked to “longer periods of immunological protection or memory.”

“As well as providing evidence for flexibility in deployment, these results suggest this approach can also help generate better immune responses,” Snape said. “This has implications beyond COVID-19 and will inform new approaches to immunization against other diseases that are, as yet, not vaccine-preventable.”

In the U.S., the Centers for Disease Control and Prevention has issued guidance allowing people to mix and match booster shots.