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