Yellow Fever Vaccine
Introduction to Yellow Fever Vaccine
Yellow fever is a potentially fatal mosquito-borne viral disease endemic in tropical regions of Africa and South America. Vaccination is the most effective preventive measure against yellow fever. This section provides an overview of the yellow fever vaccine and its significance in public health.
Key Points:
- Yellow fever is caused by a flavivirus transmitted primarily by Aedes aegypti mosquitoes
- The disease can cause severe hepatitis, hemorrhagic fever, and has a high mortality rate (20-50% in severe cases)
- The yellow fever vaccine has been available since the 1930s and is considered one of the most effective vaccines ever developed
- Vaccination is crucial for residents in endemic areas and travelers to these regions
- The vaccine is a requirement for entry into many countries, particularly in Africa
Yellow Fever Vaccine Characteristics
The yellow fever vaccine is a live attenuated vaccine that has been in use for decades. This section details the vaccine's composition, production, and available formulations.
Vaccine Composition
- Contains live attenuated 17D-204 strain of yellow fever virus
- Grown in embryonated chicken eggs
- Does not contain adjuvants or preservatives
Available Formulations
- YF-VAX (Sanofi Pasteur): Used in the United States and many other countries
- Stamaril (Sanofi Pasteur): Used in many countries outside the U.S.
- Other WHO-prequalified vaccines: Produced in Brazil, Russia, and China
Vaccine Storage
- Must be stored at 2-8°C (35-46°F)
- Protected from light
- Reconstituted vaccine should be used within 60 minutes or discarded
Yellow Fever Vaccine Administration
Proper administration of the yellow fever vaccine is crucial for its effectiveness. This section covers dosing, route of administration, and considerations for different populations.
Dosing and Schedule
- Single 0.5 mL dose for most individuals
- Historically, boosters were recommended every 10 years
- Since 2016, WHO states that a single dose provides lifelong protection for most people
Route of Administration
- Subcutaneous injection, preferably in the upper arm
- Can be given simultaneously with other vaccines, but at different injection sites
Special Populations
- Children: Can be given from 9 months of age (or 6 months during epidemics)
- Pregnant women: Generally contraindicated, but may be given if travel to high-risk area is unavoidable
- Immunocompromised individuals: Contraindicated; requires careful risk assessment
- Adults ≥60 years: Higher risk of serious adverse events; requires careful risk assessment
Booster Doses
- May be considered for certain high-risk groups:
- Laboratory workers handling live yellow fever virus
- Persons traveling to high-risk areas
- Individuals who received the vaccine while pregnant
- Those who received the vaccine while infected with HIV
Efficacy and Safety of Yellow Fever Vaccine
The yellow fever vaccine is known for its high efficacy and generally good safety profile. This section summarizes key data on vaccine effectiveness and potential adverse events.
Efficacy
- Seroconversion rates: >99% in controlled trials
- Immunity develops within 10 days for 80-100% of recipients, and within 30 days for 99% of recipients
- Provides effective protection against all known strains of yellow fever virus
- Duration of immunity: Lifelong for most recipients after a single dose
Safety Profile
- Generally well-tolerated
- Common mild reactions:
- Low-grade fever, headache, myalgia (5-15% of recipients)
- Injection site reactions
- Rare serious adverse events:
- Yellow fever vaccine-associated neurotropic disease (YEL-AND): 0.4-0.8 per 100,000 doses
- Yellow fever vaccine-associated viscerotropic disease (YEL-AVD): 0.3-0.4 per 100,000 doses
- Risk of serious adverse events increases with age, particularly in first-time recipients ≥60 years
- Allergic reactions: Rare, but can occur (especially in individuals with egg allergies)
Contraindications and Precautions
- Absolute contraindications:
- Severe allergic reaction to a previous dose or vaccine component
- Immunosuppression (including symptomatic HIV infection or CD4 count <200 cells/mm³)
- Thymus disorder or thymectomy
- Infants <6 months old
- Precautions (require risk-benefit assessment):
- Adults ≥60 years receiving vaccine for the first time
- Pregnancy
- Breastfeeding
- Infants 6-8 months old
- Asymptomatic HIV infection with CD4 count 200-499 cells/mm³
Recommendations for Yellow Fever Vaccination
Recommendations for yellow fever vaccination vary based on geographic risk, travel plans, and individual factors. This section outlines general guidelines and considerations for vaccine use.
Endemic Country Recommendations
- WHO recommends inclusion in national immunization programs in countries at risk
- Typically administered to children at 9-12 months of age in these countries
- Mass vaccination campaigns may be conducted during outbreaks
Traveler Recommendations
- Recommended for travelers to yellow fever endemic areas in Africa and South America
- Required for entry into certain countries, even if only in transit
- Vaccination should be given at least 10 days before travel to ensure immunity
- International Certificate of Vaccination or Prophylaxis (yellow card) is issued and is valid for life
Occupational Recommendations
- Laboratory workers handling live yellow fever virus
- Healthcare workers in endemic areas or those likely to care for infected patients
Risk Assessment Considerations
- Season of travel (higher risk during rainy seasons)
- Duration of travel
- Urban vs. rural travel
- Altitude (lower risk at elevations >2,300 meters)
- Individual's health status and contraindications
Vaccination Strategies in Outbreaks
- Reactive vaccination campaigns in affected areas
- Preventive vaccination in high-risk areas adjacent to outbreaks
- Consider lowering age for vaccination to 6 months during epidemics
Integration with Other Travel Health Measures
- Yellow fever vaccination should be considered alongside other travel health precautions:
- Mosquito bite prevention (use of repellents, protective clothing, bed nets)
- Other relevant travel vaccinations (e.g., hepatitis A, typhoid, meningococcal disease)
- Malaria prophylaxis if co-endemic
Yellow Fever Vaccine
- Q: What type of virus does the yellow fever vaccine protect against? A: Flavivirus
- Q: How is the yellow fever vaccine administered? A: Subcutaneous injection
- Q: How many doses of the yellow fever vaccine are typically required for long-term protection? A: One dose
- Q: After receiving the yellow fever vaccine, how long does it take for immunity to develop? A: 10-14 days
- Q: How long does immunity from the yellow fever vaccine typically last? A: Lifetime
- Q: What is the minimum age for receiving the yellow fever vaccine? A: 9 months
- Q: Which organization issues the International Certificate of Vaccination or Prophylaxis (ICVP) for yellow fever? A: World Health Organization (WHO)
- Q: In what year was the yellow fever vaccine first developed? A: 1937
- Q: What is the name of the strain used in most yellow fever vaccines? A: 17D
- Q: Which continent has the highest risk of yellow fever transmission? A: Africa
- Q: What is the typical incubation period for yellow fever? A: 3-6 days
- Q: What percentage of severe yellow fever cases are fatal without treatment? A: 50%
- Q: What insect is the primary vector for yellow fever transmission? A: Aedes aegypti mosquito
- Q: How often does the WHO recommend booster doses of yellow fever vaccine for most individuals? A: No longer recommended (since 2016)
- Q: What is the storage temperature requirement for the yellow fever vaccine? A: 2-8°C (35-46°F)
- Q: Which organ is primarily affected in severe yellow fever cases, leading to jaundice? A: Liver
- Q: What color is the liquid of the reconstituted yellow fever vaccine? A: Light orange to pink-brown
- Q: How quickly must the reconstituted yellow fever vaccine be used? A: Within 6 hours
- Q: What is the typical dosage of the yellow fever vaccine for adults and children over 9 months? A: 0.5 mL
- Q: In what year did the WHO launch the Yellow Fever Initiative to combat the disease? A: 2006
- Q: What is the name of the international regulations that govern the use of yellow fever vaccination certificates? A: International Health Regulations (IHR)
- Q: How long before travel to an endemic area should the yellow fever vaccine be administered? A: At least 10 days
- Q: What is the term for the rare but serious neurological reaction that can occur after yellow fever vaccination? A: Yellow fever vaccine-associated neurotropic disease (YEL-AND)
- Q: What percentage of yellow fever cases are asymptomatic? A: Approximately 80%
- Q: In which two continents is yellow fever endemic? A: Africa and South America
- Q: What is the fatality rate for severe yellow fever vaccine-associated viscerotropic disease (YEL-AVD)? A: 60%
- Q: What animal reservoir plays a role in the sylvatic cycle of yellow fever in South America? A: Non-human primates
- Q: How many countries required proof of yellow fever vaccination for entry as of 2022? A: Approximately 40
- Q: What is the typical duration of protection provided by the yellow fever vaccine in immunocompromised individuals? A: 10 years (may require booster)
- Q: What organization maintains the global stockpile of yellow fever vaccines for emergency response? A: International Coordinating Group (ICG) on Vaccine Provision
