Administration of yellow fever (YF) vaccine is contraindicated in infants less than 6 months old because of the risk of vaccine-associated encephalitis. A woman in Brazil transmitted yellow fever virus to her infant by breastfeeding after being vaccinated following delivery.



(1) There is a history of a live virus yellow fever vaccine being administered to the mother.

(2) The mother breastfeeds her infant.

(3) The infant presents with yellow fever.

(4) The virus infecting the infant is the vaccine strain.


Factors modifying the risk:

(1) IgG antibodies against YF in the mother transmitted transplacentally during the pregnancy


Clinical findings in the infant:

(1) fever

(2) refusal to nurse

(3) irritability

(4) seizures

(5) evidence of meningoencephalitis


Breast milk can be tested for YF virus.


Differential diagnosis:

(1) yellow fever from mosquito bite (would not be the vaccine strain)

(2) accidental vaccination of the infant with yellow fever virus (includes YF contamination of another vaccine)


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