One must also consider the frequency of feedings and volume of breast milk ingested when considering bioavailability. Of note, variations occur in an infant’s ability to metabolize, excrete, and respond to medications (ie, idiosyncratic reactions, allergic sensitization). 10 Premature and full-term infants

may not have full renal and liver function and some infants have immature GI function. Thus, it is essential to evaluate the infant’s ability to handle small amounts of medication before prescribing a medication for a breastfeeding woman. Vaccination during breastfeeding protects the mother from vaccine-preventable diseases, indirectly protects the infant by preventing maternal infection, and prevents infection in subsequent pregnancies. 1 Research is needed regarding possible changes in the immune BLZ945 cell line response of breastfeeding women as for pregnant women. Additional questions relevant to vaccinating breastfeeding women are: (1) transfer of live microbes (viruses or bacteria); (2) transfer of specific antibodies that find protocol aid or block

immunologic response in infant; and (3) transfer of chemicals used in the vaccines. The major concern regarding live vaccines is that microbes, although attenuated, might pass through breast milk to an infant with little or no immunity. This is the case with smallpox, which can be associated with severe consequences. Among women immunized with rubella vaccine (RA27/3), >69% shed the virus in breast milk, which led to IgA antibodies to rubella in breast milk. 12 Animal and human studies suggest that IgA antibodies in mammary glands, colostrum, and breast milk are induced by specific

antigens followed by migration of antigen-reactive precursor cells from intestinal and/or bronchial lymphoid tissues. 12 In 50% of the immunized women, rubella vaccine virus persisted in breast Parvulin milk up to 10–17 days postimmunization. 13 Of breastfed infants, 56% had rubella virus from nasopharynx or throat (0% in non-breastfed infants) and 25% had transient seroconversion to rubella virus without clinical disease (0% in non-breastfed infants). 13 Therefore, breastfeeding is not a contraindication or precaution to rubella vaccination. In a study of varicella vaccine, 12 postpartum women received varicella vaccine at least 6 weeks after delivery, and all seroconverted. 14 Over 200 samples of breast milk tested by polymerase chain reaction for varicella vaccine virus were negative, and all infants remained seronegative. 14 Although small, this study supports postpartum vaccination of susceptible women without interruption of breastfeeding. The second concern is that antibody transferred via human milk may interfere with the infant’s response to childhood immunizations, especially oral vaccines.