Mothers that are exposed to infection even before pregnancy may pass on lifelong immunity to their offspring via the transfer of immune cells in breastmilk even after breastfeeding stops (animal study).

This study found that infant mice that were breastfed by a mother who had been infected with a worm before becoming pregnant acquired life-long protection against this infection. This life-long immunity was acquired through immune cells that were transferred in breastmilk.

It was previously thought that the immunity benefits that infants acquire only last as long as they are breastfed but this new study suggests that the benefits may be life-long.