Why Yellow Fever Is Back in the Headlines—And What Travelers Need to Know

A friend recently asked me if it was safe to travel to Colombia while recovering from cancer. Their concern was yellow fever, not crime or altitude.

The CDC has issued a Level 2 travel alert—“Practice Enhanced Precautions”—due to increased yellow fever activity in Colombia, Peru, and Bolivia. If you’re planning to travel to one of these countries, especially areas near forests or jungles, you may need a yellow fever vaccine. And if your last dose was over 10 years ago, you might even need a booster.

What Is Yellow Fever and How Does It Spread?

Yellow fever is a viral infection transmitted by mosquitoes, particularly Aedes species. These are the same mosquitoes that spread dengue, chikungunya, and Zika. Together, these are known as vector-borne diseases. The virus has both an urban and jungle (sylvatic) transmission cycle, meaning it can spread between people in cities or jump from infected monkeys in forests to humans via mosquito bites.

Many people infected with yellow fever have no symptoms, but in severe cases, it causes high fever, liver damage, jaundice (which gives the disease its name), and bleeding. There is no cure—only supportive care—and in the most serious cases, it can be fatal.

What You Can Do to Stay Safe from Yellow Fever?

1. Get vaccinated before travel

If you’re visiting a yellow fever–endemic area, get the yellow fever vaccine at least 10 days before departure. Carry an International Certificate of Vaccination (often called the “yellow card”) as proof, since many countries—particularly in Africa and South America—require it for entry.

2. Take mosquito precautions

Use insect repellent with DEET, wear long sleeves and pants, and stay in well-screened or air-conditioned accommodations to reduce mosquito exposure. Mosquitoes that transmit yellow fever tend to bite during the day, particularly around dawn and dusk. Minimize outdoor exposure during these hours if possible.

3. Monitor your health after travel

If you experience symptoms such as fever, chills, muscle pain, headache, or jaundice after returning from a yellow fever–risk area, seek medical attention immediately and inform your healthcare provider of your travel history.

4. Stay informed and proactive

Follow public health updates and be aware of emerging outbreaks. Yellow fever is a reminder that environmental changes can lead to the spread of infectious diseases—preparedness is key.

Is Climate Change Driving an Increase in Yellow Fever?

Mosquito-borne diseases are surging globally, and climate change plays a major role. As temperatures rise, mosquito habitats expand into new areas. Urbanization and deforestation increase the chances of people coming into contact with infected animals and insects. And, when health systems are under strain, outbreaks are harder to contain.

How contagious is yellow fever?

Yellow fever is not contagious from person to person through direct contact like coughing, sneezing, or touching. Instead, it is transmitted through the bite of an infected Aedes or Haemagogus mosquito, which becomes a carrier after biting a person or primate infected with the virus. Because humans don’t spread the virus directly to one another, outbreaks depend heavily on mosquito populations and environmental conditions.

The U.S. Has Its Own Yellow Fever History

Yellow fever isn’t new to the Americas. In 1793, Philadelphia lost 10% of its population to a yellow fever epidemic. Mosquito control, vaccine development, and eventually the widespread use of air conditioning (which reduced indoor mosquito bites) transformed the outlook, and the force of infection declined in the U.S. and other countries in the Americas. But the disease hasn’t disappeared, and as the planet warms, the risk of outbreaks in previously unaffected areas grows.