To begin with, I was told not to take anything while I was breast-feeding and to lay off caffeine, chocolate, alcohol etc. An experimental “vaccine” should give anyone pause.
I am sure this mother is beside herself with grief and will probably blame herself for the rest of her life.
However, I would BELIEVE that any nursing mother would consult her doctor prior to taking ANYTHING that would affect her baby.
That being said, we know there are moms who smoke crack while pregnant. This was in New Mexico where a large part of the population is Native Americans. NA have some of the highest alcoholism and drug use in the USA.