YF-Vax Side Effects: What to Expect and When to Call Your Doctor

The yellow fever vaccine (YF-Vax) is considered safe and effective for most travelers. For the vast majority of people who receive it, side effects are mild and resolve on their own within a few days. But because YF-Vax is a live virus vaccine, it carries a small — but real — risk of rare serious adverse events that every patient should know about before vaccination.

This guide covers what's normal, what to watch for, and exactly when to call your doctor.

Common Side Effects After YF-Vax (Normal and Expected)

Mild reactions occur in a minority of recipients, typically beginning 5–7 days after vaccination and resolving within a few days. Common side effects include:

Headache

Muscle aches (myalgia)

Low-grade fever

Fatigue and malaise

Soreness, redness, or pain at the injection site

Mild swelling (edema) at the injection site

These reactions are typically self-limited and do not require medical treatment. Acetaminophen or ibuprofen can help manage discomfort. Avoid aspirin, which can increase bleeding risk.

Allergic Reactions: What to Watch For

YF-Vax contains chicken and egg proteins, gelatin, and other stabilizers. People with known egg or chicken protein allergies are at higher risk of allergic reactions. Immediate hypersensitivity reactions can include:

Rash or hives (urticaria)

Itching

Asthma/wheezing

Anaphylaxis (life-threatening allergic reaction) — rare

If you have a history of egg or gelatin allergy, inform your provider before vaccination. Skin testing with a diluted vaccine preparation may be performed before proceeding. Anaphylaxis requires immediate emergency treatment.

Serious Side Effects: YEL-AND and YEL-AVD

These are the two rare but serious adverse events associated specifically with the yellow fever vaccine:

Yellow fever vaccine-associated neurologic disease (YEL-AND): A rare condition that includes meningoencephalitis, acute disseminated encephalomyelitis, and Guillain-Barré syndrome. Onset typically occurs 2–56 days after vaccination. Incidence is 0.8 per 100,000 doses overall (2.2 per 100,000 in people aged 60+). YEL-AND is rarely fatal.

Yellow fever vaccine-associated viscerotropic disease (YEL-AVD): A severe, potentially fatal illness in which the vaccine virus replicates in multiple organs, causing multiorgan dysfunction. Onset is typically within 1–10 days of vaccination. Incidence is approximately 0.3 per 100,000 doses overall; it rises to 1.2 per 100,000 in patients aged 60+. Case-fatality ratio is approximately 43%.

These serious adverse events occur almost exclusively in first-time vaccine recipients and in people with specific underlying conditions. They are not the same as getting yellow fever itself — they are immune or viral responses to the live attenuated vaccine virus.

Who Is at Higher Risk of Serious Side Effects?

The following groups have a higher risk of serious adverse events after YF-Vax:

People aged 60 years and older: Both YEL-AND and YEL-AVD occur at significantly higher rates in this age group. The decision to vaccinate should include a careful risk-benefit discussion.

Infants 6–8 months: Vaccination is a precaution in this age group due to risk of encephalitis. Infants under 6 months should not receive the vaccine.

Immunocompromised individuals: Including those with HIV/AIDS, certain cancers, or those on immunosuppressive therapy. YF-Vax is contraindicated for severe immunodeficiency.

Thymus disorders: Including myasthenia gravis and thymoma — these are absolute contraindications.

When to Call Your Doctor After Getting YF-Vax

Call your doctor or go to the emergency room immediately if you experience any of these symptoms within 30 days of receiving YF-Vax:

High fever or severe headache

Confusion, disorientation, or altered mental status

Jaundice (yellowing of the skin or eyes)

Muscle weakness, difficulty walking, or abnormal sensations (possible Guillain-Barré)

Signs of organ failure: decreased urination, abdominal pain, severe bleeding

Anaphylaxis: hives, difficulty breathing, swelling of the throat — call 911 immediately

Adverse events following vaccination can be reported to the Vaccine Adverse Events Reporting System (VAERS) at 1-800-822-7967 or vaers.hhs.gov.

For more information, read what is YF-Vax and how it works and YF-Vax drug interactions.