What is flu?
Flu, or influenza, is a common infectious viral illness spread by coughs and sneezes.
Flu will often get better on its own, but it can make some people seriously ill.
If you are at increased risk from coronavirus, you are also more at risk of problems from flu. Research shows that if you get both viruses at the same time, you are more likely to be seriously ill.
Cold weather can make some health problems worse and even lead to serious complications, especially if you are 65 or older, or if you have a long-term health condition.
Find out more about keeping you and your family well this winter (NHS).