There is a claim that infants gain immunoprotection from breastfeeding. I am especially interested in specific protection against pathogens the breastfeeder (not necessarily the mother) has been vaccinated against intramuscularly.
While I know, that IgA and IgM may be present in breast milk and provide passive protection against foodborne pathogens, it is unclear to me, whether there would be any synthesis (and transport to breast milk) of those antibodies without contact between the pathogen and a mucosal membrane of the breastfeeder. Answer to my previous question suggest that there would be no IgA production as signals received by B-cells in a muscle will lead mostly to IgG synthesis.
I am not asking about the transplacental transport of IgG, only about breastfeeding.