Yellow Fever Explained Simply: What It Is and Why Travellers Need to Know

If you are going on a trip, you might hear the words “yellow fever” and “vaccine certificate.” This can sound confusing. So let’s break it down into simple parts.

This guide explains what yellow fever is, how people catch it, why some countries ask for proof of vaccination, and who should get extra advice before deciding.

What is Yellow Fever?

Yellow fever is an illness caused by a tiny germ called a virus. You cannot see it without a microscope.

It is called “yellow” fever because it can sometimes turn a person’s skin and eyes slightly yellow when they are very unwell. This happens because it can affect the liver, which is an organ inside your body that helps clean your blood.

Most people who catch it will only feel mildly unwell, a bit like flu. But for a small number of people, it can become serious. That is why doctors take it seriously, especially for travellers.

How do people catch it?

You cannot catch yellow fever from another person, like a cold. You catch it from the bite of a certain type of mosquito that carries the virus.These mosquitoes live in parts of Africa and parts of South America. They do not live in the UK.

So the risk mostly applies to people who are travelling to, or living in, those parts of the world.

What does the illness feel like?

A smaller number of people can become more seriously unwell after this, with symptoms affecting the liver and other organs. This is why prevention is important, and why a vaccine exists.

Why do some countries ask for a vaccination certificate?

Some countries want to stop the virus from spreading into new areas. So they ask travellers to show proof that they have already been vaccinated, using an official yellow fever certificate.

This is sometimes required:

• To enter certain countries where yellow fever exists
• To travel onward to certain other countries, even if you are just passing through
• As part of visa or border requirements

The rules are different for each country, and they can change. Because of this, it’s important to check the specific requirements for your destination before you travel, rather than assuming.

What is the yellow fever vaccine?

The vaccine is an injection. It helps your body learn how to fight the virus before you ever come into contact with it.

For most people, one dose gives long-lasting protection, and a valid certificate is usually accepted for life once ten days have passed since the vaccination.

A trained clinician needs to check that the vaccine is suitable for you first. This is because it may not be right for everyone, including:

This is why a proper assessment always comes before a yellow fever vaccination — it is not simply given to everyone automatically.

What should I do before travelling?

If you are planning a trip to a country where yellow fever exists, it’s a good idea to:

Can I do anything else to reduce my risk?

Alongside vaccination where appropriate, simple habits can help lower your risk of mosquito bites in affected areas, such as:

Quick questions people often ask