Letter: Y

Yellow fever is a mosquito-borne viral infection endemic to rural areas of sub-Saharan Africa and tropical regions of South America. The yellow fever vaccine is a live attenuated vaccine indicated for providing active immunisation for people travelling to, or residing within, yellow fever endemic areas, or countries which require an International Certificate of Vaccination and those handling potentially infectious material (e.g. laboratory personnel).

Live vaccines including the yellow fever vaccine are generally contraindicated in pregnancy due to the theoretical risk of strain reversion and congenital infection following gestational exposure. Unvaccinated pregnant women are therefore advised to avoid travelling to yellow fever endemic areas and handling potentially infected material. Where travel or contact is unavoidable, vaccination in pregnancy should be considered on a case-by case basis, weighing up the possible fetal risks of vaccination against the risk to both mother and fetus from yellow fever infection which is associated with significant morbidity and mortality, particularly in immune-naïve individuals.

The available published data are limited to approximately 690 unique cases of intrauterine exposure. These data do not currently demonstrate an increase in risk of adverse pregnancy outcomes or congenital infection following gestational exposure to yellow fever vaccine. However, the data are currently too limited to exclude the possibility.

Following vaccination against yellow fever, positive immunity is usually acquired within ten days. However, evidence from a small sample of pregnant women has suggested that gestational stage at vaccination can affect seroconversion. Women vaccinated in the third trimester should therefore be vigilant in identifying symptoms of infection following potential exposure.