Should COVID-19 vaccines be mixed?
According to The New York Times, health experts were “shocked” when the United Kingdom made a change to its guidelines in January to suggest that COVID-19 vaccines could be mixed.
The updated guidance said people could receive a different vaccine for their second dose if the vaccine they received for their first shot was unavailable.
The guidance was not based on scientific data, the Times noted, although researchers at the University of Oxford have started a trial in which they will give participants one dose of the Pfizer-BioNTech vaccine and one dose of the vaccine made by AstraZeneca.
“I think it is a good idea to see whether pairing different vaccines enhances immunity and protection,” Paul A. Offit, MD, director of the Vaccine Education Center at The Children's Hospital of Philadelphia, told Healio. “I don't think it's a good idea to do this on your own prior to studies.”
Amesh A. Adalja, MD, senior scholar at the Johns Hopkins Center for Health Security, said the need for such measures in the United States is low from an operational standpoint because the U.S. has enough supply of vaccine. However, he said there could be cause for mixing and matching under certain circumstances.
“The CDC does have guidance for extraordinary circumstances [that says] people can mix and match the Pfizer and Moderna vaccines which are, to my mind, mostly interchangeable anyway, because of the technology,” he said, referring to the messenger RNA (mRNA) platforms used by the vaccines.
“I think if someone really wants to get a second dose [of mRNA vaccine] and they cannot find the [original vaccine], I don't think it's a bad idea to just to let them have the other mRNA vaccine,” Adalja said.
He said the Oxford trial could answer some important questions without having to design a new vaccine.
“We're in an emergency situation where we're vaccinating with the first vaccines that were available and they look really good. But could they be better?” Adalja said. “Could they have a longer duration of immunity? Once we figure out what the duration of immunity is, could they have better protection against certain problematic variants?”
Kathryn M. Edwards, MD, FIDSA, scientific director of the Vanderbilt Vaccine Research Program, has a lot of experience with what she called “mix and match” studies. She agreed that it is important to look at different combinations of vaccines, saying “we really don't have any information about the immune responses when you mix them and match them.”
The need to “mix and match” may arise, however.
“You may get one vaccine, and then that vaccine may not be available, or you may move to another area,” Edwards said. “There are also people who have reactions or side effects” — such as anaphylaxis — “from one vaccine as opposed to the other. We may say don't get the mRNA vaccine again, but it's OK to go ahead and get the Johnson & Johnson vaccine,” which is a recombinant vector vaccine that uses a modified human adenovirus.
Edwards said modifying CDC guidance would take data showing that mixing vaccines works, is immunogenic and is not associated with significant side effects.
“The most important thing that we need to say is that people need to get vaccinated,” Edwards said. “The best dose and kind of vaccine to get is the one that you can get the fastest.”