Yes, artificially fed babies have a less intense response to vaccines
and develop lower titers than their normal, breastfed counterparts.

Oral polio is the only vaccine commonly given that has a theoretical
concern about breastmilk interference:  maternal polio IgA in the milk
could theoretically interfere with the exposure needed to cause the baby
to make antibodies.  This is not clinically important, though, as
breastfed babies do develop adequate polio titers.  I suppose colostrum
might have enough IgA to interfere, but we don't use oral polio before 2
months anyway, and with the new guidelines don't use the oral prep until
at least 6 months (inactivated polio is given for the first two doses).

Re:  other vaccines such as measles:  this is maternal IgG, which has
crossed the placenta during pregnancy, not related to breastfeeding.  The
reason the age has dropped from 15 months to 12 months is that most
mothers now (in the US) have had the vaccine rather than the disease, so
the mother's antibody levels are lower and less gets transferred to the
baby.  Babies' protection from maternal antibody goes away sooner, and
they can make their own antibodies at a younger age. (When there's a
measles outbreak, sometimes they recommend vaccinating people as young as
6 months.)

--
Anne Montgomery, M.D., I.B.C.L.C.
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St.Peter Hospital Family Practice Residency
Olympia, WA