If the vaccines are for the same antigen (eg the spike protein), i would expect that to work fine. Your B cells don't care how the RNA encoding the proteins got

If the vaccines are for the same antigen (eg the spike protein), i would expect that to work fine. Your B cells don't care how the RNA encoding the proteins got into your cells, just what the protein looks like. A caveat here is that different vaccines might use different versions or modifications of the spike protein, in which case it's possible they wouldn't boost each other. This feels unlikely, though, because i think that would also reduce their effectiveness against the real virus.