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Yellow fever
The Disease
Yellow fever is a viral disease which occurs in parts of Africa and South America (see
countries with yellow fever risk). It is caused by a flavivirus. The viruses that cause West Nile
fever, dengue fever, and tickborne encephalitis are also part of this virus group.
People can get yellow fever if they are bitten by a mosquito carrying the virus, typically an
Aedes or Haemagogus species mosquito. Very rarely, the virus can also spread if someone
receives blood from an infected person. Only a handful of such cases have been documented.
Although some people infected with yellow fever only have a mild illness, others develop a
serious toxic form of the disease. There is no treatment. About half of all serious cases are fatal,
especially if the person does not have medical care.
Symptoms
Some people never develop symptoms after being infected. For those who do become ill, the
first signs usually appear three to six days after the infectious mosquito bite. These are often a
sudden headache and fever, and "flu-like" symptoms that can include sensitivity to light, chills,
joint and muscle pain, and sometimes vomiting. Most people recover thereafter, though some
will develop a serious toxic form of the disease. This can involve jaundice, which turns the skin
and eyes yellow (hence the name "yellow fever"), with hemorrhagic (bleeding) symptoms and
organ failure. Between 20%-50% of people who have a severe case of yellow fever die from
the disease.
Treatment
There is no specific treatment for yellow fever. Patients are made more comfortable with
medications that may lessen their symptoms, but they cannot cure the disease.
Risk to Travelers
The risk of acquiring yellow fever is higher in Africa than in South America, but the risk varies
greatly according to location and season. In West Africa, the most dangerous time of the year is
late in the rainy season and early in the dry season (July-October). Transmission is highest
during the rainy season (January-March) in Brazil. However, people can get the disease any
time of year.
Getting vaccinated: requirements and recommendations
There are two concerns regarding yellow fever. One is risk of infection: this is a potentially
deadly disease with no cure. Travelers need to protect themselves from infection. The other is a
public health issue: travelers who are infected can carry the virus with them to other areas that
are currently free of yellow fever. If someone has the virus in their blood, and then is bitten by
a mosquito, the virus enters the mosquito population. Infected mosquitoes could then spread the
virus to the next people they bite. In this way, travelers could potentially introduce the disease
to a vulnerable population and start an outbreak.
To reduce the public health threat, many nations worldwide require travelers to show proof
they have been vaccinated against yellow fever before they will be allowed to enter the country.
Vaccination may be required if :
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You have recently visited a country in an endemic zone.
You are visiting a country that requires travelers to be vaccinated.
You are visiting a region with known yellow fever risk.
In these cases, a signed and stamped International Certificate of Vaccination or Prophylaxis
(ICVP) is required. Consult a travel health professional several weeks before your trip.
These international requirements are designed to protect your destination from the disease.
They are not necessarily aimed at protecting you from infection. To protect yourself, you
should not only consider the requirements, but whether vaccination is recommended for you by
a qualified travel health professional. Consider vaccination if you will travel to a country where
yellow fever is present. Regardless of your vaccination status, you should also take every
precaution to prevent mosquito bites.
Vaccination
Yellow fever vaccine is a live virus vaccine that has been used for several decades. It usually
provides long-term protection within a week. If a person is at continued risk of yellow fever
infection, a booster dose is needed every 10 years.
Most people do not have any side effects following yellow fever vaccination. Those who do
feel unwell after vaccination generally develop mild symptoms like headache, low fever and
muscle pain. These can last about a week.
The vaccine is only administered at designated yellow fever vaccination centers. Your local
health department can usually provide you with the locations. After vaccination, travelers
receive a vaccination certificate. It is valid beginning 10 days after the vaccination and remains
valid for 10 years.
Who should not receive the yellow fever vaccine?
(for detailed information. consult the Yellow Fever Vaccination article)
There are some groups of people who are generally advised not to have a yellow fever vaccine.
These people must make a decision in collaboration with their healthcare providers,
weighing the risk of infection against the risk of adverse events following vaccination.
If someone is ineligible for vaccination, they might decide to change their itinerary to avoid
yellow fever risk areas or delay travel until a time when they can be vaccinated. If
someone decides to travel unvaccinated, they may require a waiver letter to gain entry to
certain countries.
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Infants under six months of age should never be vaccinated against yellow fever.
Ideally, babies should not be vaccinated until they are at least nine months old.
Pregnant or breast-feeding women should discuss their individual situations with
their healthcare providers, as the risks and efficacy of vaccination in these women is not
entirely established.
Allergies can make people ineligible for vaccination. This is especially a concern for
people with egg hypersensitivity or allergies to chicken protein or gelatin. Again,
vaccination may be possible, but needs to be discussed with a qualified travel health
professional. People who are sensitive to latex, which is used in the vial stopper,
should notify their providers.
Immunosuppressed people are generally not good vaccination candidates. Some
diseases - such as AIDS or symptomatic HIV, some cancers, etc. - affect a person's
immune system. Certain medications and treatments (radiation and chemotherapy, for
example) can also cause immunosuppression.
People who have a history of thymus disorder are at increased risk for severe reactions
to the yellow fever vaccine.
If you have one of these conditions, your healthcare provider will be able to help you decide
whether you should be vaccinated, delay your travel plans or obtain a waiver. He or she will
weigh your risk 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 people who cannot be vaccinated for medical
reasons. The US Centers for Disease Control (CDC) recommends obtaining written waivers
from consular or embassy officials before departure. Travelers should contact the embassy or
consulate for specific advice.
Typically, the embassy or visa requires a letter from a doctor written on letterhead stationary
stating why the patient should not be vaccinated. The letter should bear the stamp used by a
health department or official immunization center to validate the International Certificate of
Vaccination.
CDC map of yellow fever areas in Africa and South America
CDC Yellow Fever Information
CDC Yellow Fever Comprehensive Vaccination Guidelines