Can vaccines for Covid-19 be mixed and matched?
Health experts say that the two doses should be of the same vaccine.
At the moment, coronavirus vaccines being developed in the United States, Britain and other parts of the world require two doses a few weeks apart.
In the United States, where Pfizer-BioNTech and Moderna are distributed, health authorities say the vaccines are not interchangeable. In Great Britain, where Pfizer-BioNTech and AstraZeneca and the University of Oxford are used, officials say the doses should be consistent.
But in the unlikely scenario that the same type is not available or it is unknown which one was applied first, UK authorities say it is okay to inoculate the one that is available in the second dose. Since the two given there work similarly, they argue that it is better to combine mismatched doses than the partial protection that the first injection would offer.
But in the absence of studies, vaccine doses should not be mixed, said Naor Bar-Zeev, a vaccine expert at Johns Hopkins University.
If people accidentally get a different vaccine in the second dose than they were given in the first by accident, it is likely “that it works well and is well tolerated,” but evidence is needed to be sure, Bar-Zeev added.