All vaccines except the live, replication-competent smallpox vaccine (ACAM2000, Emergent Biosolutions) and yellow fever vaccine may be given to people who are breastfeeding.

ACAM2000 is contraindicated due to the theoretical risk of contact transmission of the vaccine virus from mother to child.

The only yellow fever (YF) vaccine licensed in the United States (YF-Vax, Sanofi) is contraindicated in people who are breastfeeding infants younger than 9 months of age. There have been three case reports of YF vaccine-associated encephalitis in infants under one month of age who were being exclusively breastfed at the time the mother received YF vaccine. ACIP currently recommends that people who are breastfeeding should be advised to postpone travel to YF endemic or epidemic regions; however, if travel cannot be avoided or postponed, the breastfeeding parent should receive YF vaccine. Although there are no data, some experts recommend that breastfeeding people who receive YF vaccine should temporarily suspend breastfeeding, pump, and discard pumped milk for at least 2 weeks after vaccination before resuming breastfeeding.