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Booster Doses - Mix or Match

The NIH NIAID reported preliminary results from an ongoing study of mixed and matched booster doses.  There were 458 subjects in 3 primary groups.  One group was vaccinated with Moderna (2 doses), one received Pfizer (2 doses) and the 3rd one received J and J (one dose).  At least twelve weeks after their primary vaccination, and without any history of a Covid-19 infection, each of the 3 groups were further divided into 3 groups (about 50 each) and those groups each received a booster dose- either Moderna, Pfizer, or J and J.  Thus there were 9 final groups.  For example, the group vaccinated with Moderna could have been boosted with Moderna at half the original dose (homologous), or Pfizer (heterologous). or J and  J (heterologous).

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Preliminary Results:  There was an anamnestic antibody response with all of the boosters, but the study wasn't set up to compare the antibody and neutralizing antibody titers among groups.  In addition, the cellular component of an immune response (memory B cells and T cells) is being analyzed, but is not yet complete. 

But there were no differences between the reactogenicity, local and systemic symptoms, in the heterologous vs the homologous booster doses and most were mild. Knowing that the mixing of vaccines is safe makes this a possibility moving forward.  There are many ways that this will make the booster dose easier to deliver:  patients who may have had an allergic reaction to one of the vaccines can be given one of the others.  It also will make it easier to go into a congregant care facility and boost all patients with just one vaccine type.  The FDA and CDC will now have to analyze and approve this plan to mix and match!  Stay tuned for the final approval and ongoing booster plans to be determined by the CDC and their scientific advisory committee.


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