Mixing and Matching Vaccines

I wrote a big long post laying out the advantages and disadvantages of taking AZ or mRNA after getting a first dose of AZ. That advice was BC-focused, and included considerations about vaccine availability.

This page includes some material from that posting, but focuses on scientific findings about the effectiveness of mixing vs. matching, as opposed to trying to help you make a decision between AZ or mRNA.


Side effects

  • The Com-CoV study found AZ+Pfizer side effects were still mild, meaning “no lasting damage and over pretty quickly”, but possibly quite unpleasant.
  • The tiny Ulm study said that the side effects were “in line with previous reports” and that the Pfizer second shot side effects weren’t as bad as the AZ first shot. (I believe that with AZ+AZ, the first dose’s side effects are worse than the second.) They did not compare AZ+AZ directly to AZ+Pfizer.
  • The small Berlin study said basically the same thing as the tiny German study.
  • The Saarland study found that the side effects of a Pfizer dose after an AZ dose were about the same as Pfizer after Pfizer.
  • This study from Saarland University Medical Center with 216 vaccinees found that side effects were worse for AZ than mRNA on the first dose, but AZ+mRNA was fine and very similar to mRNA+mRNA.