Yellow fever is a disease caused by an arbovirus (yellow fever virus), which is commonly found in Africa and South America. Yellow fever is spread through the bite of an infected mosquito. This disease cannot be transmitted through touch. Blood tests can detect yellow fever antibodies produced in response to the infection.

• Once contracted, the virus incubates in the body for 3-6 days. The first phase of infection usually causes fever, muscle pain, headache, loss of appetite, nausea, and vomiting. Most patients improve and their symptoms disappear after 3-4 days.
• A small percentage of patients enter a second phase, more toxic phase within 24 hours of recovering from initial symptoms. High fever returns and several body systems are affected, usually the liver and the kidneys. In this phase people are likely to develop jaundice (yellowing of the skin and eyes, hence the name ‘yellow fever’), dark urine and abdominal pain with vomiting. Bleeding can occur from the mouth, nose, eyes or stomach. Half of the patients who enter the toxic phase die within 7-10 days.
• There is currently no specific anti-viral drug for yellow fever. Yellow fever is prevented by getting yellow fever vaccine and preventing mosquito bites.

Yellow fever vaccine

The yellow fever vaccine is a live attenuated vaccine. It is given as a single shot. One dose provides lifelong protection for most people. The vaccine provides effective immunity within 10 days for 80-100% of people vaccinated and within 30 days for more than 99% of people vaccinated. It should be administered at least 10 days before traveling to a country considered to be in the yellow fever zone. 

 

Who should get yellow fever vaccine?

• People 9 months through 59 years of age who are traveling to or living in areas at risk for yellow fever virus activity, or traveling to a country with an entry requirement for vaccination.
• Laboratory personnel who might be exposed to yellow fever virus or vaccine virus.

Who should not get yellow fever vaccine?

• Anyone with a severe (life-threatening) allergy to eggs, or chicken proteins, or gelatin, or who has had a severe allergic reaction to a previous dose of yellow fever vaccine.
• Infants younger than 6 months of age (as it increases the risk of contracting meningitis).
• Adults 60 years of age and older (as side effects can be more serious than in those younger).
• Infants 6-9 months of age, pregnant women, and nursing mothers should avoid or postpone travel to an area where there is a risk of yellow fever. If travel cannot be avoided, discuss vaccination with your doctor.

Tell your doctor if:

• You have HIV/AIDS or another disease that affects the immune system.
• You are receiving immunosuppressant medication, such as steroids or chemotherapy drugs.
• You have had thymus removed or been diagnosed with a thymus disorder.
• You may be vaccinated if you have minor illnesses, such as a cold. If you have moderately or severely ill, you should usually wait until recover before getting yellow fever vaccine.

What are undesirable effects of the yellow vaccine?

• Common side effects: Pain, swelling or redness at the injection site (found in 1 out of 4 persons).
• Serious side effects:
  • Severe allergic reaction (hives, swelling of the face and throat, difficulty breathing, a fast heartbeat, dizziness, or weakness)
  • Nervous system reactions such as inflammation of the brain (encephalitis) and/or spinal cord covering (meningitis), or Guillain-Barré Syndrome (GBS), among others.
  • Life-threatening severe illness with organ dysfunction or failure.

In regions where yellow fever is endemic. The severe adverse events following immunization’ (AEFI), when the vaccine provokes an attack on the liver, the kidneys or on the nervous system are rare between 0 and 0.21 cases per 10,000 doses. 

The Necessity of Yellow Fever Vaccine for Travelers

You should be vaccinated at least 10 days before travelling to endemic areas of yellow fever. After getting the vaccine, you will be given an “International Certificate of Vaccination or Prophylaxis” (ICVP, sometimes called the “yellow card”). You will need this card as proof of vaccination to enter certain countries.
If you cannot get yellow fever vaccine for medical reasons and you are traveling to a country with a yellow fever vaccination entry requirement, your doctor will need to fill out the Medical Contraindications to Vaccination section of your yellow card. 

Interaction with other medical products

• Yellow fever vaccine can be administered simultaneously with other inactivated or live vaccines, given at the same visit but separate injection sites.
• If two or more live vaccines are not administered during the same visit, they should be separated by 4 weeks or more. With an exception, an oral typhoid vaccine can be administered simultaneously with or at any interval before or after other live vaccines (injectable or intranasal) if indicated.
• Do not donate blood for 14 days after vaccination, because there is a risk of passing vaccine virus to others during that period.

References

• World Health Organization. Yellow fever. Available from: https://www.who.int/news-room/fact-sheets/detail/yellow-fever [Accessed 1 February 2022].
• Centers for Disease Control and Prevention. Yellow Fever Vaccine Information Statement. Available from: https://www.cdc.gov/vaccines/hcp/vis/vis-statements/yf.html [Accessed 1 February 2022].
• Centers for Disease Control and Prevention. Timing and Spacing of Immunobiologics: General Best Practice Guidelines for Immunization: Best Practices Guidance of the Advisory Committee on Immunization Practices (ACIP). Available from: https://www.cdc.gov/vaccines/hcp/acip-recs/general-recs/timing.html [Accessed 1 February 2022].