From the Guidelines
Yellow fever is a viral disease transmitted by infected mosquitoes, characterized by symptoms that develop in two phases, and prevention is crucial, primarily relying on vaccination with a single dose of the yellow fever vaccine, which provides lifelong immunity, as recommended by the Advisory Committee on Immunization Practices (ACIP) 1, 2. The disease is caused by a flavivirus that damages the liver and other organs, explaining the jaundice and potential for severe complications, including death in 20-50% of severe cases. Initial symptoms include:
- Fever
- Headache
- Muscle pain
- Nausea
- Vomiting
- Fatigue After a brief remission, about 15% of patients enter a more severe phase with:
- Jaundice (yellowing of skin and eyes)
- Abdominal pain
- Bleeding
- Organ failure There is no specific antiviral treatment for yellow fever; care focuses on managing symptoms with pain relievers like acetaminophen (avoiding aspirin and NSAIDs due to bleeding risk), maintaining hydration, and providing supportive care for organ function. Severe cases require hospitalization for intensive supportive care. Additional preventive measures include:
- Using insect repellent containing DEET
- Wearing long-sleeved clothing
- Staying in screened or air-conditioned accommodations
- Eliminating mosquito breeding sites The risk for acquiring yellow fever is difficult to predict because of variations in ecologic determinants of virus transmission, but the estimated risks for illness and death attributable to yellow fever for an unvaccinated traveler traveling to an area of West Africa where the disease is endemic are 50 and 10 cases per 100,000 population, respectively; for South America, the risks for illness and death are five cases and one case per 100,000 population, respectively 3. The yellow fever vaccine is recommended for those traveling to or living in endemic regions in Africa and South America, and vaccination is the most effective way to prevent yellow fever, with a single dose providing lifelong immunity 1, 2.
From the Research
Symptoms of Yellow Fever
- The disease has an incubation period of 3 to 6 days and sudden onset of symptoms with high fever, myalgia, headache, nausea/vomiting and increased transaminases 4.
- The disease ranges from asymptomatic to severe forms, with the most serious forms occurring in around 15% of those infected, leading to renal, hepatic and neurological impairment, and bleeding episodes 4.
Treatment of Yellow Fever
- Treatment of mild and moderate forms is symptomatic 4.
- Severe and malignant forms depend on intensive care 4.
Prevention of Yellow Fever
- Prevention is achieved by administering the vaccine, which is an effective (immunogenicity at 90-98%) and safe (0.4 severe events per 100,000 doses) measure 4.
- The vaccine seems safe in people being treated with immunomodulatory or immunosuppressive therapy, people with immunosuppressive diseases, and solid organ and hematopoietic stem cell transplant patients 5.
- HIV-infected patients with a CD4+ count > 200 cells/mm3 do not have increased risk of adverse events from the vaccine 5.
- Egg allergy vaccination protocols seem to provide a safe way to immunize these patients 5.
Adverse Events Associated with Yellow Fever Vaccination
- Rare reports of serious adverse events (SAE) following vaccination have prompted the Advisory Committee for Immunization Practices to periodically expand the list of conditions considered contraindications and precautions to vaccination 6.
- The reporting rate for anaphylaxis was 1.3 per 100,000 doses distributed and was highest in persons ≤18 years (2.7 per 100,000) 6.
- Reporting rates of YEL-AND and YEL-AVD were 0.8 and 0.3 per 100,000 doses distributed, respectively; both rates increased with increasing age 6.
- The mechanism(s) of serious adverse events is(are) poorly understood, but advances in understanding the immune response induced by the vaccine have promise to help elucidate the mechanism of serious adverse events 7.