Yellow fever is more than just a fever. It is a potentially life-threatening viral disease spread through the bite of an infected mosquito. The 'yellow’ in the name refers to the jaundice that affects some patients.

While Southern Africa has historically experienced fewer yellow fever outbreaks than West or Central Africa, the risk remains. Gaps in vaccination coverage, population movements and urbanisation can create the conditions for outbreaks to spread quickly. Vaccination is one of the most effective ways to prevent yellow fever and stop outbreaks before they escalate. For communities at risk, timely vaccination and a rapid response can make the difference between containing an outbreak and watching it grow.

 

What are the symptoms of yellow fever? 

There is no specific antiviral treatment for yellow fever, making prevention essential. Symptoms usually appear three to six days after infection and can range from mild to severe.

Early symptoms may include:

• Fever
• Chills
• Headache
• Muscle pain
• Nausea
• Vomiting

For some people, the disease progresses to a severe, or toxic, phase that can be fatal. Symptoms at this stage may include jaundice, which causes the skin and eyes to turn yellow, abnormal bleeding, and liver and kidney failure.

How is yellow fever spread? 

Yellow fever is transmitted through the daytime bite of infected Aedes mosquitoes. These mosquitoes can transmit the virus after becoming infected, helping to spread the disease between people. In tropical forests, yellow fever can also circulate between mosquitoes and primates, with humans becoming infected when bitten by an infected mosquito.
 

How can you protect against yellow fever?

1. Getting vaccinated - The yellow fever vaccine provides long-lasting protection and is a key tool in preventing and controlling outbreaks.The yellow fever vaccine is safe, affordable, and highly effective. A single dose gives lifelong protection for most people, with protective immunity developing within 10 to 30 days
2. Preventing mosquito bites - Use insect repellent, wear clothing that covers the skin, and use mosquito nets where appropriate.
3. Reducing mosquito breeding sites - Removing standing water and other potential breeding sites can help reduce mosquito populations.
4. Raising awareness - Health education and community engagement help people understand the risks of yellow fever, recognise symptoms and learn how to protect themselves.

How does Doctors Without Borders (MSF) respond to yellow fever emergencies?

When outbreaks happen, our teams move fast, focusing on the following: 

1. Containing outbreaks - We help contain epidemics through large-scale vaccination campaigns and community-wide insecticide spraying to reduce the spread of infected mosquitoes.
2. Patient care - MSF provides treatment for people with severe yellow fever and supports health facilities to manage complicated cases.
3. Support to local health facilities - During outbreaks, we work alongside national and local health authorities by preparing hospitals, strengthening case management, and training healthcare workers.
4. Vaccine access - Doctors Without Borders maximises the impact of limited vaccine supplies and advocates for more vaccines and stronger routine immunisation coverage.
    

2015: The biggest outbreak in numbers

The largest yellow fever outbreak of the past 30 years began in Angola in December 2015 and spread to the neighbouring Democratic Republic of Congo (DRC). We took part in the emergency vaccination response in both countries.

In recent times, epidemics have developed in forested areas or around water points. In Angola, however, the outbreak developed in the capital, Luanda, which had been spared for decades and where there were no mosquitoes carrying the virus.

The disease was probably brought to Luanda by a person who had contracted it in the forest, or who brought in the eggs of mosquitoes carrying the virus. The outbreak therefore began with a limited number of infected people and mosquitoes. However, the epidemic affected a very popular market visited by people from across the city, who then spread the virus.

By the time the outbreak was discovered and a response could be put in place, the number of cases among humans had risen, and consequently, so had the number of infected mosquitoes. The epidemic then spread to other provinces and, through travellers, to countries including China and Kenya, and later to the DRC.

•    MSF mobilised 100 teams – 160 people – from 20 countries.
•    65 vehicles transported the teams where they were needed most.
•    In Kinshasa, DRC, we vaccinated 760,000 people, about 10% of the city’s target population.
•    In Matadi, near the Angolan border, 69 teams vaccinated 370,000 residents in just 10 days.
 

What to remember

• Yellow fever remains a serious, vaccine-preventable disease that is endemic in Africa and has the potential to spread in Southern Africa. 
• Lifesaving strategies, including mass vaccination campaigns, mosquito control, and rapid outbreak responses, are key. 
• Doctors Without Borders (MSF) continues to work with communities, governments, and global health partners to reduce yellow fever transmission and save lives.