First time posting here (joined recently)
The science around BF & immunity is still very much a work in progress but it’s fascinating (if you’re a nerd, like me).
Breast milk will contain antibodies against pathogens (disease-causing organisms) to which the mother has been exposed naturally or via vaccination. That much is straightforward.
Next, as the infant starts to explore his/her environment, initially via crawling, he/she will encounter various new potential germs. Given the mother’s instinct to kiss her child’s head (& hands) she will sample some of what he/she comes across in the environment and antibodies will be produced which will quickly find their way into her milk.
Finally, at the end of each suck, a small amount of the baby’s saliva will back flow into the breast. Antibodies are produced following exposure to this “sample” which the baby will then ingest during future feeds. Research has shown that that there are antibodies in breast milk which aren’t present elsewhere in the mother’s body - but are present in her baby - and this is the hypothesis that has been suggested to explain this.
In Ashley’s situation, as I understand it, Tommy got sick first, then she & Alf got poorly around the same time? Given the highly infectious nature of gastroenteritis and that they all live closely together, it’s likely that Ashley’s body was already mounting an immune response soon after Tommy got sick but even if that didn’t happen, it would have done as soon as Alf got sick thanks to the “back flow”.
What’s important to remember is that formula fed babes (with a normal immune system) will mount their own immune response and recover that way. We all get there.
Edit to remove repeated paragraph