Researcher says science backs mixing
A mix of two different vaccine platforms likely enhances immunity, Dr. Kedl said. The heterologous prime-boost strategy has been used in animal studies for decades, “and it is well known that this promotes a much better immune response than when immunizing with the same vaccine twice.
“If you think about it in a Venn diagram sort of way, it makes sense,” he said in an interview. “Each vaccine has a number of components in it that influence immunity in various ways, but between the two of them, they only have one component that is similar. In the case of the coronavirus vaccines, the one thing both have in common is the spike protein from SARS-CoV-2. In essence, this gives you two shots at generating immunity against the one thing in each vaccine you care most about, but only one shot for the other vaccine components in each platform, resulting in an amplified response against the common target.”
In fact, the heterologous prime-boost vaccination strategy has proven to be effective in humans in early studies.
For example, an Ebola regimen that consisted of an adenovirus vector, similar to the AstraZeneca COVID vaccine, and a modified vaccinia virus vector showed promise in a phase 1 study. And an HIV regimen that consisted of the combination of a DNA vaccine, similar to the Pfizer and Moderna mRNA vaccines, and another viral vector showed encouraging results in a proof-of-concept study.
In both these cases, the heterologous prime-boost strategy was far better than single-vaccine prime-boost regimens, Dr. Kedl pointed out. And neither study reported any safety issues with the combinations.
For now, it’s best to stick with the same manufacturer for both shots, as the CDC guidance suggests, he said, agreeing with Dr. Poland.
But “I would be very surprised if we didn’t move to a mixing of vaccine platforms for the population,” Dr. Kedl said.
A version of this article first appeared on Medscape.com.