Yellow
Fever
Yellow
fever occurs only in
Africa and South America. In South America sporadic infections occur almost
exclusively in forestry and agricultural workers from occupational exposure in
or near forests.
In Africa the virus is
transmitted in three geographic regions:
- principally and
foremost, in the moist savanna zones of West and Central Africa during the
rainy season,
- secondly, outbreaks
occur occasionally in urban locations and villages in Africa,
- and finally, to a
lesser extent, in jungle regions.
Yellow fever is a viral
disease transmitted between humans by a mosquito. Yellow fever is a very rare
cause of illness in travelers, but most countries have regulations and
requirements for yellow fever vaccination that must be met prior to entering the
country. General precautions to avoid mosquito bites should be followed. These
include the use of insect repellent, protective clothing, and mosquito netting.
Yellow fever vaccine is a live virus vaccine which has been used for several
decades. A single dose confers immunity lasting 10 years or more. Adults and
children over 9 months can take this vaccine. Administration of immune globulin
does not interfere with the antibody response to yellow fever vaccine. This
vaccine is only administered at designated yellow fever vaccination centers; the
locations of which can usually be given by your local health department. The CDC
does not keep a list of registered yellow fever vaccination sites. If a person
is at continued risk of yellow fever infection, a booster dose is needed every
10 years.
Note: Vaccination
recommendations have recently changed (MMWR
Nov. 8, 2002). In addition, there have been
recent
reports documenting patients between 1996 and 2001 who developed severe illness
potentially related to yellow fever vaccination.
Who Should Not Receive
the Yellow Fever Vaccine?
Yellow fever vaccine
generally has few side effects; fewer than 5% of vaccinees develop mild
headache, muscle pain, or other minor symptoms 5 to 10 days after vaccination.
Under almost all circumstances, there are four groups of people who should not
receive the vaccine unless the risk of yellow fever disease exceeds the small
risk associated with the vaccine. These people should obtain either a waiver
letter prior to travel or delay travel to an area with active yellow fever
transmission:
- Yellow fever vaccine
should never be given to infants under 6 months of age due to a risk of viral
encephalitis developing in the child. In most cases, vaccination should be
deferred until the child is 9 to 12 months of age.
- Pregnant women should
not be vaccinated because of a theoretical risk that the developing fetus may
become infected from the vaccine.
- Persons hypersensitive
to eggs should not receive the vaccine because it is prepared in embryonated
eggs. If vaccination of a traveler with a questionable history of egg
hypersensitivity is considered essential, an intradermal test dose may be
administered under close medical supervision. (Notify your doctor prior to
vaccination if you think that you may be allergic to the vaccine or to egg
products.)
- Persons with an
immunosuppressed condition associated with AIDS or HIV infection, or those
whose immune system has been altered by either diseases such as leukemia and
lymphoma or through drugs and radiation should not receive the vaccine. People
with asymptomatic HIV infection may be vaccinated if exposure to yellow fever
cannot be avoided.
If you have one of these
conditions, your doctor will be able to help you decide whether you should be
vaccinated, delay your travel, or obtain a waiver. In all cases, the decision to
immunize an infant between 6 and 9 months of age, a pregnant woman, or an
immunocompromised patient should be made on an individual basis. The physician
should weigh the risks of exposure and contracting the disease against the risks
of immunization, and possibly consider alternative means of protection.
Medical Waivers
Most countries will
accept a medical waiver for persons with a medical reason for not receiving the
vaccination. CDC recommends obtaining written waivers from consular or embassy
officials before departure. Travelers should contact the embassy or consulate
for specific advice. Typically, a physician's letter stating the reason for
withholding the vaccination and written on letterhead stationery is required by
the embassy or consulate. The letter should bear the stamp used by a health
department or official immunization center to validate the International
Certificate of Vaccination.
Yellow fever vaccination
requirements and recommendations for specific countries are available from the
CDC Travelers' Health page.
