Yellow fever vaccine
|Target disease||Yellow fever|
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Yellow fever vaccine is a vaccine that protects against yellow fever. Yellow fever is a viral infection that occurs in Africa and South America. About 99% of people develop immunity within one month of vaccination and this appears to be lifelong. The vaccine can be used to control outbreaks of disease. It is given either by injection into a muscle or just under the skin.
The World Health Organization (WHO) recommends routine immunization in all countries where the disease is common. This should typically occur between nine and twelve months of age. Those travelling to areas where the disease occurs should also be immunized. Additional doses after the first are generally not needed.
Yellow fever vaccine is generally safe. This includes in those with HIV infection but without symptoms. Mild side effects may include headache, muscle pains, pain at the injection site, fever, and rash. Severe allergies occur in about eight per million doses, serious neurological problems occur in about four per million doses, and organ failure occurs in about three per million doses. It is likely safe in pregnancy and therefore recommended among those who will be potentially exposed. It should not be given to those with very poor immune function.
Yellow fever vaccine came into use in 1938. It is on the World Health Organization's List of Essential Medicines, the most important medication needed in a basic health system. The wholesale price is between 4.30 and 21.30 USD per dose as of 2014. In the United States it costs between 50 and 100 USD. The vaccine is made from weakened yellow fever virus.
People most at risk of contracting the virus should be vaccinated. Woodcutters working in tropical areas should be particularly targeted for vaccination. Insecticides, protective clothing, and screening of houses are helpful, but not always sufficient for mosquito control; people should always use an insecticide spray while in certain areas. In affected areas, mosquito control methods have proven effective in decreasing the number of cases.
Travelers should have the vaccine 10 days prior to being in an endemic area.
On 17 May 2013, the World Health Organization (WHO) Strategic Advisory Group of Experts on immunization (SAGE) announced that a ‘booster’ dose of yellow fever (YF) vaccine, ten years after a primary dose, is not necessary. Since yellow fever vaccination began in the 1930s, only 12 known cases of yellow fever post-vaccination have been identified, after 600 million doses have been dispensed. Evidence showed that among this small number of “vaccine failures”, all cases developed the disease within five years of vaccination. This demonstrates that immunity does not decrease with time. 
The World Health Organization recommends the vaccine between the ages of 9 and 12 months in areas where the disease is common. Anyone over the age of 9 months who has not been previously immunized and either lives in or are travelling to an area were the disease occurs should also be immunized.
The yellow fever 17D vaccine is considered very safe with over 500 million doses given and very few documented cases of vaccine associated illness. In no case of vaccine related illness has there been evidence of the virus reverting to a virulent phenotype.
The majority of adverse reactions to the 17D vaccine result from allergic reaction to the eggs in which the vaccine is grown. Persons with known egg allergy should discuss this with their physician prior to vaccination. In addition, there is a small risk of neurologic disease and encephalitis, particularly in individuals with compromised immune systems and very young children. The 17D vaccine is contraindicated in (among others) infants between 0–6 months or over 59 years of age, people with Thymus disorders associated with abnormal immune cell function, people with primary immunodeficiencies, and anyone with a diminished immune capacity including those taking immunosuppressant drugs.
There is a small risk of more severe yellow fever-like disease associated with the vaccine. This reaction, called YEL-AVD, causes a fairly severe disease closely resembling yellow fever caused by virulent strains of the virus. The risk factor/s for YEL-AVD are not known, although it has been suggested that it may be genetic. The 2`-5` oligoadenylate synthetase (OAS) component of the innate immune response has been shown to be particularly important in protection from Flavivirus infection. In at least one case of YEL-AVD, the patient was found to have an allelic mutation in a single nucleotide polymorphism (SNP) of the OAS gene.
The Canadian Medical Association published a 2001 CMAJ article entitled "Yellow fever vaccination: be sure the patient needs it". The article begins by stating that of the 7 people who developed system failure within 2 to 5 days of the vaccine in 1996–2001, 6 died "including 2 who were vaccinated even though they were planning to travel to countries where yellow fever has never been reported." The article cites that "3 demonstrated histopatholic changes consistent with wild yellow fever virus." The author recommends vaccination for only non-contraindicated travelers (see the articles list) and those travelers going where yellow fever activity is reported or in the endemic zone which can be found mapped at the CDC website cited below. In addition, the 2010 online edition of the Center for Disease Control Traveler's Health Yellow Book that between 1970 and 2002 only "nine cases of yellow fever were reported in unvaccinated travelers from the United States and Europe who traveled" to West Africa and South America, and 8 of the 9 died. However, it goes on to cite "only 1 documented case of yellow fever in a vaccinated traveler. This nonfatal case occurred in a traveler from Spain who visited several West African countries in 1988".
In 1937, Max Theiler, working at the Rockefeller Foundation, developed a safe and highly efficacious vaccine for yellow fever. This vaccine was first used in 1938 in Brazil. For his work on the yellow fever vaccine, he received the 1951 Nobel Prize in Physiology or Medicine.
The vaccine is made from weakened yellow fever virus. This weakened type of virus is known as 17D and the vaccine based on it has been used commercially since the 1950s. The mechanisms of attenuation and immunogenicity for the 17D strain are not known.
- "Vaccines and vaccination against yellow fever. WHO position paper -- June 2013." (PDF). Releve epidemiologique hebdomadaire / Section d'hygiene du Secretariat de la Societe des Nations = Weekly epidemiological record / Health Section of the Secretariat of the League of Nations 88 (27): 269–83. 5 July 2013. PMID 23909008.
- Staples, JE; Bocchini JA, Jr; Rubin, L; Fischer, M; Centers for Disease Control and Prevention, (CDC) (19 June 2015). "Yellow Fever Vaccine Booster Doses: Recommendations of the Advisory Committee on Immunization Practices, 2015.". MMWR. Morbidity and mortality weekly report 64 (23): 647–50. PMID 26086636.
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- "Center for Disease Control and Prevention – Vaccine Information Statements (VIS)".
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- Bae HG, Domingo C, Tenorio A, et al. (June 2008). "Immune response during adverse events after 17D-derived yellow fever vaccination in Europe". J. Infect. Dis. 197 (11): 1577–84. doi:10.1086/587844. PMID 18419548.
- Weir, E (October 2001). "Yellow fever vaccination: be sure the patient needs it". CMAJ : Canadian Medical Association 165 (7): 941. PMC 81520. PMID 11599337.
- Mark Gershman, Betsy Schroeder, and J. Erin Staples. "Yellow Fever". Yellow Book. Center for Disease Control (Canada). Retrieved 1 July 2011.
- "Max Theiler – Biography". Retrieved 2009-01-15.