Infant and maternal immunity linked

During breastfeeding a child presents to the mother's immune system the germs it encounters in the environment - by way of its mouth.

Tiny travellers may enter mother's bloodstream, for example when baby suckles hard or nips mama.  In turn, these activate mam's own well-trained immune defenses and baby receives a nourishing supply of the proper IgA from mama within minutes to hours to days... as long as the antigenic challenge exists.