How is it caught?
Measles can be caught through direct contact with an infected person, or through the air via droplets from coughs or sneezes.
It can affect people at any age - although having measles once usually means lifelong immunity to catching it again.
Measles does mainly affect young children, and complications are more common among children under five, those with weakened immune systems or a poor diet.
The main symptoms of measles are:
- Cold-like symptoms
- A distinctive red-brown rash
2013 is expected to be the worst year for measles in the UK for the past two decades. Read more about the illness and how it is treated.
If the Government's top adviser on immunisation thinks the risk of an emergency in England is a possibility, I believe him.