About pandemic flu
A flu virus is classed as a pandemic when:
- a new type of the flu virus develops
- most people have no immunity against the virus – this means they may not be able to fight the infection
- humans are affected and can pass the flu virus on to others
- the virus spreads quickly and easily around the world
An epidemic is when more people are affected by a disease than usual. A pandemic is a worldwide epidemic.
Pandemic flu is similar to seasonal flu – the normal type of flu that tends to happen at around the same time every year – but the symptoms can be more severe. This is because few people will be able to fight off the infection easily, as it is significantly different to previous strains of flu they have had.
More people are infected with the flu virus during a pandemic than are affected by seasonal flu. Seasonal flu tends to affect people in the winter, but pandemic flu can happen at any time of the year.
In the twentieth century there have several flu pandemics, including the Spanish flu outbreak in 1918 and 1919 that killed millions of people around the world. In 2009 there was a flu pandemic of the H1N1 flu virus (swine flu).
It’s difficult to predict when a pandemic will happen, which virus might cause it or how many people might be affected. Pandemic flu can affect anyone, even the fit and healthy.
The proteins that make up the flu virus are constantly changing (mutating). A flu pandemic can occur if there is a more dramatic change to the flu virus than is normally seen every year. This can happen if there is a mix of types of flu from different species, such as birds or pigs, with a human strain of flu. This is called an antigenic shift. This mix of different viruses can make a new, unique virus that no one will be immune to.
Flu viruses are very infectious. Most people catch flu by breathing in air that has the virus in it. This usually happens when people with flu cough or sneeze, which spreads the virus in the air.
You can also catch flu through direct contact with someone who has it, for example by shaking hands or by touching something they have touched. If you pick up the flu virus on your hands and then touch your nose or mouth, you may infect yourself. The flu virus can live on hard surfaces for up to 24 hours and on soft surfaces for about 20 minutes.
If you have flu, you are infectious and can spread the virus to other people, from the day when your symptoms start to five days afterwards. Children are infectious for longer.
Complications of pandemic flu
Healthy adults usually recover completely from seasonal flu in a few weeks. However, when pandemic flu develops it’s difficult to know how severe the infection will be or how it may affect people. This is because the virus is new. Some groups of people may be affected more than others.
The complications of flu can include:
- conditions that affect your lungs, for example, pneumonia and bronchitis
- worsening of chest conditions such as asthma
- middle ear infections
- inflamed sinuses (sinusitis)
Young children can sometimes have seizures or fits called febrile convulsions. These are caused by their high body temperature.