We delayed our kids' shots until after 1yo, because we watched this happen to my sibling's kid: went in for a round of routine shots, then the same evening ran a 106-degree fever, ended up in the ER. Then pediatrician gaslit them about it, insisted it was nothing to do with the shots... and the same thing happened TWO MORE TIMES with the next two rounds of routine shots. And the doc STILL insisted it was not related.

So when I had kids I was like... let's wait til they're older, and let's only get one shot at a time, so if anything like that happens, at least we'll know which shot caused it, and we can say "no" to that one going forward.