Interest in mix-and-match vaccine approach picks up steam

June 29, 2021

A new study has pointed to potential benefits for mixing the AstraZeneca COVID-19 shot with other vaccines. 

Called Com-COV, the study compared two different schedules of the AstraZeneca vaccine in combination with Pfizer’s shot. No matter which sequence of vaccines was used, the outcome was a higher concentration of antibodies and more protection against the coronavirus. Overall, two Pfizer doses performed the best in terms of efficacy. But a schedule of mixed shots that produced the highest T cell response and the most antibodies was the AstraZeneca vaccine followed by a dose from Pfizer.

Although the lead Oxford professor behind the trial said that it was not large enough to warrant major regulatory changes to approved vaccine schedules, many countries in the EU have begun to push alternatives to the AstraZeneca vaccine due to concerns over rare blood clots.

Meanwhile, worries about variants have prompted several health care experts to try mixing jabs as well.

Last week, a virologist at the University of Saskatchewan tweeted that she had chosen to “top off” her J&J vaccine with a Pfizer shot. She also encouraged others who got the J&J shot to pursue a follow-up vaccine of another type to potentially provide more protection against the Delta variant that now accounts for an estimated 20% of new cases in the U.S. 

It is still unclear exactly how well the J&J protects against the Delta variant — the most contagious strain of the virus that has been detected — but early studies suggest that it could be about 60% effective.

Given those concerns, another infectious disease expert recently told Reuters that he had also gotten an mRNA booster on top of his J&J jab — and a handful of other experts have followed suit. J&J, meanwhile, is also studying whether or not a booster of its shot could provide additional immunity to COVID-19.