Dr. Susan Kuhn of the University of Calgary says this incident affirms current recommendations breastfeeding mothers avoid the yellow fever vaccine -- in use since the 1940s -- because it is a live-virus vaccine.
"Until recently, avoidance of vaccination of breastfeeding women with yellow fever vaccine had been based on theoretical grounds only," Kuhn and colleagues say in a statement.
Kuhn is among authors of a case study, published in the Canadian Medical Association Journal, that describes a previously healthy 5-week-old infant in Canada coming to the hospital with seizures on alternating sides after two days of fever and irritability.
Spinal fluid tests indicated yellow fever, but the baby received no vaccinations, had no signs of insect bites and had no contact with infected individuals.
However, when the infant was 10 days old, the mother received pre-travel vaccinations -- including one for yellow fever and subsequently traveled for one week to an urban area of Venezuela not considered at risk for yellow fever.
The authors advise women adjust plans to reduce travel exposure or postpone until an infant is no longer breast feeding or is old enough to be vaccinated.