Dear Gloria, it seems that the immunity from the disease is stronger than
the immunity from a shot The baby's prenatally acquired immunity remained
strong enough to prevent measles and interfered with the MMR if given too
soon. That was why MMR was being given after 15 mo.  However, now most
young moms are immune as a benefit of the MMR, not the disease,  and the
baby's prenatally acquired immunity wanes sooner,  so their babies need the
MMR sooner.  At least that's the way it was explained to me.  Sincerely,
Pat in SNJ