In a study of 830 older adults, mixed two-dose schedules of AstraZeneca and Pfizer vaccines produced higher concentrations of antibodies against the coronavirus that a full schedule of the AstraZeneca shot.
The most effective approach – two doses of Pfizer/BioNTech mRNA vaccine - produced levels of antibodies about 10 times higher than two doses of the AstraZeneca vaccine, the researchers reported on Friday in a Lancet preprint.
However, the AstraZeneca shot followed by a Pfizer jab induced antibody levels about as high as two Pfizer/BioNTech doses.
Giving the Pfizer shot first, followed by AstraZeneca's, was not as successful. That combination yielded antibody levels higher than two AstraZeneca shots but lower than two doses of the Pfizer vaccine.
There were no new safety issues uncovered in the study.
Matthew Snape, the Oxford professor behind the trial, said the findings could be used to give flexibility to vaccine rollouts but were not significant enough to recommend a broad shift away from clinically approved schedules.