Well, I don't know what the answer is to the question "if the baby has
a reaction" how long must the mother avoid feeding her?  It might
depend how sensitive the baby was.  You could try it, and I doubt the
baby will have a reaction, even if she remains sensitive to cow milk
protein.  We do not know how long mothers absorb whole milk protein
from the gut and excrete cow milk protein into the milk.  Maybe it's
only 6 months.

For this reason, (a negative reaction means nothing), I would
challenge the baby directly.  Not an ounce, but a few drops, or even a
drop (have some epinephrine ready).  If no problem, try again in a few
hours, or a few days with a little more and increase slowly.  If the
baby has a reaction with an ounce of milk in the stomach, you'll have
to put down an ng tube to get it out.  With one drop, no problem.  You
could even start by putting the drop of milk into the conjunctiva.

Doing all this on the same day as the immunizations will confuse the
issue a little, but if all the baby does is get fussy for a couple of
days, that is not what we are worried about, which is anaphylaxis.

Jack Newman, MD, FRCPC