Vaccines: Yellow Fever

Specific vaccination recommendations vary among countries or even within one country. Local or country-specific guidelines should be consulted.

Yellow fever virus vaccines are only available in Canada through registered vaccination centers, a list of which can be obtained from www.canada.ca.

1. Vaccines: The only vaccine authorized for use in Canada contains live attenuated viruses.

2. Indications: Vaccination is recommended, and may be compulsory, ≥10 days prior to traveling to some countries with yellow fever virus endemicity. Travelers should consult vaccination requirements at their destination ≥1 month prior to departure (see World Health Organization [WHO] recommendations). The vaccine should be administered to patients aged 9 months to 60 years traveling to areas in Africa and South America where yellow fever virus is endemic or transitional, provided there are no contraindications to administration.

3. Contraindications: Universal for all live vaccines (see Immunization and Selected Vaccinations in Adults), hypersensitivity to eggs, chicken, or any of the vaccine components, severe hypersensitivity reactions after a previous dose of the vaccine, infants aged <6 months, primary immunodeficiency, individuals after transplant, those treated with immunosuppressive medications, persons with thymus disorders (thymoma, myasthenia gravis), HIV infection (symptomatic or if CD4+ cell count <200/microL in adults), or malignancy. Circumstances requiring caution in deciding about yellow fever vaccination are age 6 to 8 months or ≥60 years, pregnancy, breastfeeding, and asymptomatic HIV infection with CD4+ cell count between 200 and 499/microL.

4. Special populations: The decision to vaccinate patients who are aged ≥60 years, are pregnant, or are breastfeeding requires shared decision making and weighing of risks and benefits. Primary vaccination should only be considered on a case-by-case basis if travel to an endemic or transitional region cannot be postponed, or if the individuals will be unable to adhere to rigorous mosquito protection measures. Those aged ≥60 years are at high risk of yellow fever vaccine–associated neurotropic disease (YEL-AND) or yellow fever vaccine–associated viscerotropic disease (YEL-AVD). Pregnant patients have low seroconversion rates, especially in the third trimester; in these patients postvaccination titers should be taken, with a level >1:10 conferring protective immunity. Women receiving their primary series while pregnant should be considered for a one-time booster dose (see below).

4. Adult vaccination schedule: A single 0.5-mL dose, administered subcutaneously. Health-care providers must document vaccination using an International Certificate of Vaccination or Prophylaxis, as required by the WHO regulations. For primary vaccination, the record becomes valid 10 days after administration of the vaccine for the whole life of the vaccinated person (this applies retroactively, including patients immunized prior to the international regulatory amendment in 2016). Booster doses in applicable populations (see below) are immediately valid once documented. The decision to vaccinate should weigh country entry requirements, the risk of infection related to the route and nature of the journey, clinical consequences in the event of illness, contraindications, and the risk of YEL-AND and YEL-AVD in a given patient.

5. Booster doses: Only recommended in selected groups at increased risk. Specifically, a one-time booster dose is recommended in travelers who were pregnant when they completed the primary series, those who have undergone a hematopoietic stem cell transplant after having completed the primary series, and those who received a fractional dose, or an incompletely or inadequately documented dose of yellow fever vaccine.

A one-time booster dose may be considered in patients traveling to a major outbreak area, particularly in West Africa, if >10 years have elapsed since completion of the primary series.

Patients living with HIV infection (unless contraindicated, see above) should receive a booster dose every 10 years if they are traveling to an endemic region.

Laboratory workers with occupational exposure to wild-type yellow fever virus should also receive a booster dose every 10 years, unless there is serologic evidence of a protective antibody titer (>1:10).

6. Adverse events: Local injection site reactions are common, and so are systemic adverse events such as headache (31.4%), myalgia (25.1%), and fever (14.0%).

YEL-AND is a rare vaccine-associated adverse event occurring at a rate of 0.8 per 100,000 doses, with the rates being highest in those aged ≥60 years and <9 months. Death from YEL-AND is rare. YEL-AND typically occurs between 7 and 21 days following vaccination and can include a spectrum of manifestations such as meningoencephalitis, Guillain-Barré syndrome, acute bulbar palsy, and acute disseminated encephalomyelitis.

YEL-AVD is a rare vaccine-associated adverse event occurring at a rate of 0.1 per 100,000 doses among those aged ≤60 years, with the rates being highest in those aged ≥60 years. Case-fatality rates are very high, particularly in women (90%) compared with men (50%).