My guess is through breast milk - which I was wondering about with the study as well; does it make a difference for breastfed babies whether their moms eat a lot of peanuts?
Anecdotal: a pregnant woman ate a lot of the stuff (something similar to Bamba) when pregnant, and I mean a lot. The child was diagnosed with peanut allergy when 1 y.o.
Solution? Peanut microdosing, increasing dose progressively, in few months the allergy was gone.
Anecdote from my partner: Allergies come and go, they're not necessarily permanent even if you don't treat them.
Since no one really knows what causes peanut allergies, it isn’t surprising they come and go without much insight into why.
Mom, dad, siblings. Anyone snacking on it will have it on their faces, finger tips. It'll get on the counters and floor. And find its way on a bottle nipple, blankets, sheets, fingers, etc.