Flu (influenza), seasonal

The flu virus is contained in the millions of tiny droplets that come out of the nose and mouth when someone coughs or sneezes.

These droplets typically spread about one metre (3ft). They hang suspended in the air for a while but then land on surfaces, where the virus can survive for up to 24 hours.

Anyone who touches these surfaces can spread the virus by touching anything else.

Everyday items at home and in public places may have traces of the virus. These include food, door handles, the remote control, handrails and computer keyboards.

People usually become infected by picking up the virus on their hands from contaminated objects and then placing their hands near their mouth or nose. It is also possible to breathe in the virus if it is suspended in airborne droplets.

Resistance and mutation

If you become infected with a flu virus your body will produce antibodies against it. Antibodies are proteins that recognise and fight off germs that have invaded your blood, such as viruses. 

Your antibodies will remember this flu virus and fight it if it invades your body again.

Over time the flu virus can mutate (change) into a different version, which means your body may not recognise it and you can catch flu again in the future.

The flu virus mutates because its structure is unstable. When the virus mutates to a new strain that people have little or no resistance to, it can cause a flu pandemic, which means it can spread globally. Go to Health A-Z: pandemic flu for more information.

Glossary

Immunity

The immune system is the body's defence system, which helps protect it from disease, bacteria and viruses.

Epidemics

An epidemic is a sudden outbreak of disease that spreads through a population in a short amount of time.