Just wanted to share this from the 1997 Red Book-Report of the Committee on
Infectious Diseases 24th Edition, American Academy of Pediatrics pp 73-74:

"Immunization of Mothers and Infants

EFFECT OF MATERNAL IMMUNIZATION

Women who have not received the recommended immunizations before or during
pregnancy may be immunized postpartum regardless of lactation status.  No
evidence exists for concern about the potential presence in maternal milk of
live virus from vaciines if the mother is immunized during lactation.
Lactating womenmay be immunized, as recommednded for other adults, to protect
against measles, mumps, rubella, tetanus, diphtheria, influenza, and hepatitis
B. If previously unvaccinated or if traveling to a highly endemic area, a
lactationg mother may be given inactivated poliovirus vaccine (IPV).  Although
rubella vaccine virus has been detected in milk after maternal immunization,
no evidence indicates that administration of rubella vaccine to the postpartum
mother has any potential for harm to the term or preterm infant.  Rubella
seronegative mothers who could not be immunized during pregnancy should be
immunized postpartum.  Whether varicella vaccine is secreted in human milk,
and if so whether it would infect the infant, is not known.  Therefore
varicella vaccine may be considered for a susceptible nursing mother if the
risk of exposure to varicella-zoster virus is high.

EFFICACY OF IMMUNIZATION IN BREASTFED INFANTS

The immunogenicity of some currently recommended vaccines is enhanced by
breastfeeding, but the importance of these observatiuons in their efficacy is
unknown.  Although high concentrations of anti-poliovirus antibody in milk fo
some mothers theoretically could interfere with the immunogenicity of oral
polio vaccine (OPV), no such association has been demonstrated.  Infants
should be immunized according to the recommended schedule regardless of the
infants' mode of feeding."

Following after this section is a nice summary of transmission of infectious
agents via human milk, human milk banks and antimicrobial agents in maternal
milk.

Hope this clarifies things,

Pierrette Mimi Poinsett MD FAAP
Modesto CA