Mixing coronavirus vaccines yields 40 times greater immune response, study finds

INDIANAPOLIS (WISH) — Combining the AstraZeneca COVID-19 vaccine dose with a Pfizer dose boosts immunity from the virus 40 times greater than one shot of the AstraZeneca vaccine alone, a new study finds. 

Researchers at the Carlos III Institute in Spain recruited 673 participants. All had been vaccinated with their first dose of AstraZeneca within the previous eight weeks. Of those participants, 403 people were given a second dose — as per the vaccine protocol — but with the Pfizer vaccine instead. The remainder of participants did not receive a second dose of either vaccine. 

Results showed those who received the AstraZeneca dose followed by a Pfizer dose had an antibody response 40 times greater compared to those who received a single dose of AstraZeneca. Data from a previous study showed the response was also higher than in people who received two doses of AstraZeneca.

“It does speak to some ideas that exist about people who might have gotten one of the available vaccines first and were trying to get the second dose with another vaccine,” Dr. Christopher Doehring, vice president of medical affairs at Franciscan Health, told News 8. “Certainly going forward when we have booster shots, we’ll have to think of how important it will be to stay with the same platform or if it will be OK to mix and match.”

Getting two shots, he says, is better than one if that is what is required, so he is not surprised by the results. 

Both the AstraZeneca and Pfizer vaccines are a two-dose regimen. 

AstraZeneca’s COVID-19 is not currently authorized in the U.S., and mixing vaccinations goes against FDA recommendations. However, moving forward, mixing vaccine doses could be useful for countries that lack supply. 


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