For what it's worth, my PCP doesn't like any vaccines taken within fewer than 14 days of another one. To me, this is nicely conservative. That way, if one has some reaction, it's easier to suspect what likely triggered it. Conceptually, a vaccine is a kind of mild insult to the body so keeping (triggering of immune system, about which we've all read in cytokine storm covid reports) so doing the least at any one time makes sense to me at least.