Flu is a respiratory illness, affecting the lungs and airways, and is the result of an infection caused by an influenza virus. Most serious illness is seen in very young babies, pregnant women, older people and those with long term health conditions.
It circulates in Wales mostly during the winter months each year. There are often slight changes to the flu virus each year which means that annual vaccination is needed for best protection.
Free annual NHS flu immunisation is available for people at most risk of complications from flu.