What causes flu (influenza)?

Flu is caused by the influenza viruses A and B.

The flu virus is usually spread when someone infected with the virus sneezes or coughs, releasing droplets that contain the virus into the air. These droplets can be breathed in by others, or transferred to anyone who touches a surface contaminated with droplets containing the virus.

You can catch the flu at any time of the year, not just in winter. You can reduce your risk of catching and spreading the flu by being vaccinated with the seasonal flu vaccine and taking simple but effective steps to prevent infection such as washing your hands with soap.

Anyone can catch the flu, but some people are at more risk of either catching the flu or of developing complications from a respiratory tract infection.