What are the risks of taking the yellow fever vaccine (YFV) more than once?

Safety of Repeat Yellow Fever Vaccination

Receiving the yellow fever vaccine more than once is generally safe, with serious adverse events occurring almost exclusively after the first dose, not with booster vaccinations. 1

Key Safety Evidence for Repeat Vaccination

The most critical safety finding is that life-threatening complications (YEL-AND and YEL-AVD) are seen almost exclusively in primary vaccine recipients, not in those receiving booster doses. 1 This means the risk profile for a second or subsequent dose is substantially lower than for the initial vaccination.

Risk Stratification by Vaccination History

First-time recipients:

• Overall serious adverse event rate: 4.7 per 100,000 doses 1
• Yellow fever vaccine-associated neurotropic disease (YEL-AND): 0.8 per 100,000 doses 1
• Yellow fever vaccine-associated viscerotropic disease (YEL-AVD): 0.4 per 100,000 doses 1

Repeat recipients:

• Serious adverse events are rare and not well-documented in surveillance data because they occur almost exclusively in primary vaccinees 1

Age-Specific Considerations for Repeat Vaccination

Adults ≥60 years receiving their FIRST dose face elevated risks:

• Serious adverse event rate: 8.3 per 100,000 doses (compared to 4.7 overall) 1
• YEL-AND: 1.8 per 100,000 doses 1
• YEL-AVD: 1.4 per 100,000 doses 1
• Risk is 7.5 times higher than in persons aged 19-29 years 1

However, this elevated risk applies specifically to first-time vaccination in older adults, not to booster doses. 1

Current Vaccination Interval Recommendations

International Health Regulations require revaccination at 10-year intervals for travel purposes, though evidence suggests immunity may last much longer. 2 To minimize any potential adverse events and optimize immune response, a 10-year interval between doses should be observed when possible. 2

Duration of Immunity Evidence

• A single dose provides strong immunity that persists for many decades and might provide lifelong protection 2, 3
• Pooled seroprotection rates 10+ years post-vaccination: 94% in healthy adult travelers 3
• Lower rates observed in specific populations: 76% in endemic areas, 47% in children vaccinated at 9-23 months, and 61% in people living with HIV 3

Practical Clinical Approach

When repeat vaccination is indicated:

1. Document previous vaccination history - If the date cannot be ascertained and vaccination is required, administer a booster dose 2

2. Observe the 10-year interval when feasible to minimize any theoretical adverse events 2

3. Reassure patients about safety - The serious complications that make headlines occur almost exclusively with first doses, not boosters 1

4. Consider individual risk factors only for FIRST-time vaccination:

   • Age ≥60 years (precaution for first dose only) 1
   • Immunosuppression (contraindication) 1
   • Pregnancy (precaution) 1
   • Breastfeeding (precaution) 1

Common Pitfall to Avoid

Do not confuse the elevated risks in first-time elderly vaccinees with risks for booster doses. The surveillance data clearly shows that YEL-AND and YEL-AVD occur almost exclusively in primary vaccine recipients. 1 A 65-year-old who received their first yellow fever vaccine at age 30 and needs a booster does not carry the same elevated risk as a 65-year-old receiving their first dose ever.

Administration Details

• Administer 0.5 mL subcutaneously at an approved Yellow Fever Vaccination Center 4, 2
• If inadvertently given intramuscularly, do not repeat the dose as immune response is likely unaffected 2
• Defer blood donation for 2 weeks post-vaccination 2
• Administer simultaneously with other live viral vaccines or 30 days apart 2