• Adverse reactions following yellow fever vaccine are typically mild and consist of headache, myalgia, low grade fever, and/or soreness at the injection site, and will occur in 10–30% of recipients.
• Injection-site reactions tend to occur from days 1–5 after immunization.
• Systemic adverse effects also occur early but may last up to 2 weeks. Up to 1% of individuals may need to alter daily activities due to these.
• Rash, urticaria, bronchospasm, and anaphylaxis occur rarely (estimated to be 1 case per 130,000 doses of vaccine).
• Post-vaccine encephalitis may occur rarely in infants under 6 months old (0.5 to 4 cases per 1000 infants under 6 months of age).
• Rarely, yellow fever vaccine-associated neurological disease (YEL-AND) may occur (4 cases per million doses given).
• YEL-AND begins 4–23 days after vaccination with the onset of fever and headache that may progress to include one or more of: confusion, focal neurological deficits, coma, and Guillain–Barré syndrome. Most people recover completely. All cases have occurred following primary vaccination (in people who have no underlying yellow fever immunity).
• Rarely, yellow fever vaccine-associated viscerotropic disease (YEL-AVD) may occur (3 cases per million doses given).
• YEL-AVD begins 2–7 days after vaccination with the onset of fever, malaise, headache, and myalgias that progress to hepatitis, hypotension, and multi-organ failure; death has occurred in more than 60% of reported cases. All cases have occurred following primary vaccination (in people without underlying yellow fever immunity). In the reports of viscerotropic disease, 17% have had a history of thymus disease with subsequent thymectomy. Thus, patients with thymus disorders should not receive yellow fever vaccine.
• For those who are aged 60 years or older, the risk of neurological and viscerotropic adverse events increases:
• Neurological events — 18 cases per million doses.
• Viscerotropic events — 22 cases per million doses.

[DH, 2006c]