I think that while it might be possible vaccines could increase SIDS, I think the main cause is much more obvious. They get smothered in mattresses and blankets and crap.

Cases of SIDS dropped around 50% in the 90s when the "Back to sleep, stomach to play" campaign was launched.

And I think they dropped again when pediatricians started recommending getting rid of crib bumpers and loose blankets and toys and all the other crap people put in cribs.

I constantly had arguments with my MIL about this when she would babysit. My youngest had poor muscle tone when he was a baby and couldn't lift his head much, and she would put him face down in the crib that had thick mattress pads with a bunch of toys and crap. And then she would tell me not to worry, because she did the same with my husband (her child) and he lived. 😡