Yellow fever virus

Background

Microbiology

• RNA virus and member of the Flaviviridae family

Epidemiology

• Worldwide, about 200,000 cases and 30,000 deaths annually

Clinical Manifestations

• Spectrum of illness from asymptomatic to fatal
• Acute illness starts with fever, chills, headache, backache, myalgias, arthralgias, nausea, vomiting, photophobia, mild jaundice, and epigastric pain
• After the acute illness subsides, about 85% of infections are resolved, and 15% progress
• In those who progress, a brief remission of hours to days is followed by return of symptoms with progression to renal failure, hemorrhage, and thrombocytopenia

Vaccine-Related Disease

• Yellow fever vaccine-associated neurotropic disease, which includes meningoencephalitis, Guillain-Barré syndrome, and acute bulbar palsy
• Yellow fever vaccine-associated viscerotropic disease, which causes multi-organ failure similar to wildtype virus

	YEL-AND	YEL-AVD
Incubation period	7 to 21 days	2 to 5 days
Rate	0.8 per 100,000 doses	1 per 100,000 doses
Risk factors	age <6 months age >60-70 years	age >60 years thymus disease
Prognosis	full recovery	65% mortality

Management

• Supportive care

Prevention

• A live attenuated vaccine strain is available, with a single dose provided at least decades of and possibly life-long immunity
• Antibodies develop within 28 days
• Contraindications
  • Allergy to any component of the vaccine
  • Immunocompromised state, including HIV with CD4 <200 or <15%, B-cell deficiency (except isolated IgA deficiency, IgG subclass deficiency, and specific antibody deficiency), and combined B- and T-cell deficiency
  • Infants less than 6 to 9 months of age, due to the high risk of neurotropic disease following immunization
  • People age 60 years and older, due to the high risk of adverse events following immunization
    • Booster doses may stll be given, if indicated
  • Pregnancy and breastfeeding
  • Thymus disease, including thymoma, thymectomy, and myasthenia gravis, given the high risk of viscerotropic disease
  • Moderate or severe acute illness
• Booster doses
  • No longer routinely indicated
  • May be indicated if the original dose was given when the recipient was unlikely to mount a full immune response
    • Vaccinated during pregnancy, while on immunosuppressants, or other immunocompromise like HIV
      • One-time booster for most, and booster every 10 years for HIV
    • Hematopoietic stem cell transplant since last vaccination
      • One-time full dose
    • Last dose was fractional, given improperly, undocumented, or underdocumented
      • One-time full dose
  • May be indicated for individuals at particularly high risk of exposure
    • Travel to an area experiencing an outbreak
    • Frequent or prolonged travel to areas with high endemicity, particularly West Africa
    • One-time booster if 10 or more years since primary vaccination
  • May be indicated for individuals with regular and ongoing exposure
    • Laboratory workers working on yellow fever virus
    • Booster every 10 years unless antibody titres confirm ongoing immunity
• Vaccination can cause YF vaccine-associated neurotropic disease and YF vaccine-associated viscerotropic disease