What is already known on this topic?
Administration of yellow fever vaccine is contraindicated in children aged <6 months because of increased risk for vaccine-associated encephalitis; the Advisory Committee on Immunization Practices cautions against vaccinating breast-feeding women to avoid the potential risk for transmission of yellow fever vaccine virus to breast-feeding infants.
What is added by this report?
This report describes laboratory-confirmed, breastfeeding–associated transmission of 17DD yellow fever vaccine virus from a recently vaccinated mother; the affected infant developed postvaccinal encephalitis requiring hospitalization.
What are the implications for public health practice?
Health-care personnel should be aware that yellow fever vaccine virus can be transmitted through breastfeeding, and administration of yellow fever vaccine to breast-feeding women should be avoided except in situations where exposure to circulating yellow fever viruses cannot be avoided.