Yellow Fever: UK Guide to Vaccination, Symptoms, and Travel Safety

Yellow fever is an acute viral haemorrhagic disease transmitted by infected Aedes aegypti and Haemagogus mosquitoes. According to the NHS and the World Health Organization (WHO), the 'yellow' in the name refers to the jaundice that affects some patients when the virus attacks the liver. While many people experience mild symptoms, the disease can be fatal in its severe form.

It is endemic in tropical areas of Africa and Central and South America. Because the virus can be carried between countries by travellers, international health regulations are strictly enforced. British travellers visiting these regions must be aware of both the health risks and the legal requirements regarding documentation.

Most people infected with the yellow fever virus do not develop symptoms, or their symptoms are very mild. However, for those who do get sick, the illness usually develops in two stages:

Phase 1: The Acute Stage

Symptoms typically appear 3 to 6 days after the mosquito bite and include:

• Sudden onset of fever and chills.
• Severe headache and back pain.
• General muscle aches (myalgia).
• Nausea, vomiting, and loss of appetite.
• Fatigue and dizziness.

Most patients recover after this phase, which lasts about 3 to 4 days.

Phase 2: The Toxic Stage

Roughly 15% of patients enter a more serious phase within 24 hours of recovering from initial symptoms. This stage involves high fever and the return of symptoms, but with damage to internal organs. Signs include jaundice (yellowing of the skin and eyes), abdominal pain, and bleeding from the nose, mouth, or eyes. NICE guidance notes that approximately half of the patients who enter this toxic phase die within 7 to 10 days.

Vaccination is the cornerstone of travel health when visiting risk areas. In the UK, the vaccine used is Stamaril, a live-attenuated vaccine. A single dose provides life-long immunity for the vast majority of people. The vaccine is highly effective, with immunity beginning to develop within 10 days of the injection.

Because it is a live vaccine, it may not be suitable for everyone, including infants under 9 months, pregnant women, or individuals with severely weakened immune systems (such as those with HIV or receiving chemotherapy). Adults over 60 who have never been vaccinated before also require a careful risk assessment by a healthcare professional due to a slightly higher risk of rare side effects.

When you travel to certain countries, you may be asked for proof of vaccination. This is provided in the form of an International Certificate of Vaccination or Prophylaxis (ICVP). This document is only valid if the vaccine was administered at an officially designated Yellow Fever Vaccination Centre (YFVC) in the UK.

Under International Health Regulations, the certificate becomes valid 10 days after the primary vaccination. If you are travelling to a country where the vaccine is a legal entry requirement, you must ensure your appointment is booked well in advance of your departure date. If you cannot have the vaccine for medical reasons, a GP or travel nurse can provide a 'Medical Exemption Certificate,' though entry is still at the discretion of the destination country.

While the vaccine is excellent, it does not protect against other mosquito-borne illnesses found in the same regions, such as Zika, Dengue, or Malaria. Therefore, all UK travellers should practice rigorous bite prevention:

• Use Repellent: Apply repellents containing at least 50% DEET to exposed skin.
• Wear Protective Clothing: Opt for long-sleeved shirts and long trousers, ideally treated with permethrin.
• Sleep Safely: Use mosquito nets if sleeping in areas that are not air-conditioned or screened.
• Timing: Be particularly vigilant during daylight hours, as the mosquitoes that carry yellow fever are most active during the day.

Navigating travel health requirements can be complex. You should speak to a GP online or book a travel consultation if you are planning a trip to Africa or South America and are unsure of the risks. An online doctor can review your medical history to see if you are eligible for the vaccine and provide advice on other necessary precautions, such as malaria tablets.

If you have recently returned to the UK from a high-risk area and develop a high fever, headache, or jaundice, you must seek medical attention immediately. While you cannot be diagnosed with yellow fever via a video call, an online GP can help triage your symptoms and direct you to the appropriate NHS secondary care or tropical medicine specialist if a serious infection is suspected.