World Health Organization Reports That 10-Year Yellow Fever Vaccine Booster Is Not Necessary
Mark D. Gershman and J. Erin Staples.
Yellow fever is a mosquito-borne disease that is endemic to sub-Saharan Africa and tropical South America. Yellow fever virus causes an estimated 200 000 cases of clinical disease and 30 000 deaths annually . Clinical disease varies from a mild, undifferentiated febrile illness to severe disease with jaundice and hemorrhage. The case-fatality ratio for severe yellow fever is 20%–50% . Because no specific treatment exists for yellow fever, prevention is critical to reduce disease risk. One of the most effective prevention measures against yellow fever is vaccination with the live attenuated yellow fever 17D substrain virus vaccine.
Yellow fever vaccine is recommended for persons aged ≥9 months who are traveling to or living in areas with risk for yellow fever virus transmission. In addition, the International Health Regulations (IHR) allow countries to require proof of yellow fever vaccination from travelers entering their country. Such requirements are intended to minimize the potential importation and spread of yellow fever virus. Proof of yellow fever vaccination is recorded on the International Certificate of Vaccination or Prophylaxis (ICVP or “yellow card”). The IHR specify that the ICVP is valid for 10 years . Therefore, if 10 or more years has elapsed since the last vaccination, people planning travel to a country with a yellow fever vaccination entry requirement need to get a booster.
New Guidance from the Strategic Advisory Group of Experts. The Strategic Advisory Group of Experts (SAGE), the principal advisory group to the World Health Organization (WHO) for vaccines and immunization, recently concluded that a single dose of yellow fever vaccine is sufficient to confer sustained immunity and lifelong protection against yellow fever disease, and a booster dose of the vaccine is not needed . This conclusion was based on a systematic review of published studies on the duration of immunity produced by yellow fever vaccine and on data that suggest vaccine failures are extremely rare and do not increase in frequency with time since vaccination. SAGE noted that future studies and surveillance data should be used to identify specific risk groups (such as infants or human immunodeficiency virus–infected patients) that could benefit from a booster dose.
Implications of the New Sage Guidance. The most significant impact of the recent SAGE guidance likely will be in endemic countries. This guidance will help countries direct potentially limited vaccine resources to ensure good primary vaccination coverage among the resident population rather than to provide booster doses. The impact of this guidance on international travel is mitigated by the fact that there has been no change in the IHR requiring a yellow fever vaccine booster every 10 years to maintain a valid ICVP. As part of the new guidance, SAGE has requested that WHO revisit the IHR provisions relating to the period of validity for the ICVP . No date has been set for revisiting the IHR provisions, but the process would require WHO to consult with all member states to elicit their feedback and approval. It would take some time before changes could be made to the IHR's booster dose requirement for yellow fever vaccine.
Editorial comment. In the United States, the Centers for Disease Control and Prevention's Advisory Committee on Immunization Practices (ACIP) makes recommendations for vaccine use. Despite the recent change in SAGE guidance, ACIP still recommends revaccination with yellow fever vaccine every 10 years for US travelers to areas with yellow fever risk to boost antibody titers . ACIP will consider the need for a booster dose when its current recommendations are updated.
Until changes are made to the IHR, countries may still require travelers to have proof of a booster dose of yellow fever vaccine to enter their country. The WHO list of these countries is available at http://www.who.int/ith/chapters/ith2012en_annexes.pdf. However, given the new SAGE guidance, national authorities will need to consider whether booster doses should continue to be recommended for their travelers who are going to a country with risk for yellow fever that does not require proof of vaccination for entry.