Risk for an individual traveler is highly variable and depends on factors such as the season, locations and duration of travel, and activities of the traveler. Limited data indicate that JE acquired during the first or second trimesters of pregnancy causes intrauterine infection and miscarriage. Infections during the third trimester of pregnancy have not been associated with adverse outcomes in newborns. Advanced age may also be a risk factor for developing symptomatic illness after JE infection.
Thimerosal is added as a preservative.
In general, vaccine should be considered for use in persons spending a month or longer in epidemic or endemic areas during the transmission season, especially if travel will include rural areas. Depending on the epidemic circumstances, vaccine should be considered for persons spending less than 30 days whose activities, such as extensive outdoor activities in rural areas, place them at particularly high risk for exposure. Vaccination during pregnancy Vaccination poses an unknown but theoretical risk to the developing fetus, and the vaccine should not be routinely administered during pregnancy. However, because JE infection acquired during pregnancy carries the potential for intrauterine infection and miscarriage, the risk of JE infection to the mother and developing fetus should be weighed against the theoretical risks of immunization for pregnant women who will travel to areas where JE is prevalent. The last dose should be given at least 10 days before beginning international travel to ensure an adequate immune response and access to medical care in the event of a delayed adverse reaction.