Who should receive the yellow fever vaccine and how often is a booster dose required?

Yellow Fever Vaccine Recommendations

Yellow fever vaccine is recommended for persons aged ≥9 months who are traveling to or living in areas of South America and Africa where yellow fever virus transmission is endemic, with booster doses no longer required for most individuals due to evidence of long-lasting immunity after a single dose. 1

Who Should Receive the Yellow Fever Vaccine

• Travelers aged ≥9 months visiting or living in areas of South America and Africa where yellow fever is endemic 1, 2
• Laboratory personnel who might be exposed to virulent yellow fever virus or concentrated preparations of the 17D vaccine strain 1
• Individuals requiring proof of vaccination for entry into certain countries, particularly in Africa, which may require evidence of vaccination from all entering travelers 1
• Persons traveling from countries known or thought to have yellow fever virus, even if only in transit, as some countries strictly enforce vaccination requirements 1

Contraindications

• Infants younger than 6 months of age due to substantially elevated risk of yellow fever vaccine-associated neurotropic disease (YEL-AND) 1
• Persons with immunodeficiency diseases including symptomatic HIV infection 1, 2
• Individuals with leukemia, lymphoma, or generalized malignancy 1, 2
• Persons immunosuppressed by therapies including:
  • High-dose systemic corticosteroids (≥20 mg/day of prednisone or equivalent for ≥2 weeks) 1
  • Alkylating drugs, antimetabolites, TNF-α inhibitors, and other monoclonal antibodies targeting immune cells 1
  • Current or recent radiation therapy 1
• History of thymus disorders including thymoma or thymus dysfunction 2, 3

Precautions

• Infants aged 6-8 months (travel to endemic areas should be postponed if possible) 1
• Adults aged ≥60 years, particularly for first-time vaccination, due to increased risk of serious adverse events 1
• Pregnant women (should only receive vaccine if travel to high-risk area cannot be avoided) 1, 2
• Persons with history of allergies to egg or other vaccine components 1, 2

Dosage and Administration

• A single subcutaneous injection of 0.5 mL of reconstituted vaccine is used for all age groups 1
• The vaccine must be administered at an approved Yellow Fever Vaccination Center 1
• Vaccinees should receive an International Certificate of Vaccination that has been completed, signed, and validated with the center's stamp 1
• The vaccine should be administered at least 10 days before travel to endemic areas to be valid for entry requirements 2

Booster Dose Requirements

• The International Health Regulations historically required revaccination at intervals of 10 years 1
• However, evidence from multiple studies demonstrates that yellow fever vaccine immunity persists for 30-35 years and probably for life 1
• Current evidence indicates that a single dose of yellow fever vaccine provides long-lasting protection and lifetime immunity against yellow fever disease for most people 1
• Some researchers have questioned whether a single dose provides lifelong protection for all individuals, suggesting that at least a second dose might be needed for full protection in some cases 4

Adverse Events

• Reactions to yellow fever vaccine are typically mild, with headaches, myalgia, low-grade fevers occurring in <25% of vaccinees 1
• Serious adverse events are rare but include:
  • Yellow fever vaccine-associated neurotropic disease (YEL-AND) 1
  • Yellow fever vaccine-associated viscerotropic disease (YEL-AVD) 1
  • Immediate hypersensitivity reactions (estimated incidence of 1/130,000-250,000) 1
• The risk of serious adverse events increases with age, particularly in those ≥60 years 1

Medical Waivers

• If travel to endemic areas cannot be avoided but vaccination is contraindicated, a medical waiver should be provided 1
• The waiver should be completed in the Medical Contraindications to Vaccination section of the International Certificate of Vaccination and Prophylaxis (ICVP) 1
• A separate signed and dated exemption letter should also be provided to the traveler 1

Additional Protective Measures

• All travelers to endemic areas, especially those with medical waivers, should take precautions to avoid mosquito bites 2, 3
• Use insect repellent containing DEET, wear permethrin-impregnated clothing, and stay in accommodations with screened or air-conditioned rooms 2
• These protective measures are critical for unvaccinated travelers, as the case-fatality rate of severe yellow fever is 20-50% 1, 5

Yellow fever vaccination remains one of the most important preventive measures for travelers to endemic regions, with a single dose providing long-lasting protection for most individuals while balancing the rare risk of serious adverse events in specific populations.