What is swine flu ?

Influenza is caused by infection with a virus. There are many types of flu virus and these are constantly changing, which makes it hard for the human immune system to deal with it. The particular type of influenza virus that causes swine flu is known as H1N1, which is a type of Influenza A (there are also influenza B and C viruses).

It is the same group of H1N1 viruses which cause the regular yearly flu outbreaks in humans, but swine flu is caused by different strains of H1N1. The current strain of swine flu has not previously been found in pigs or humans, and contains a mixture of genetic material from human, pig and bird flu. In other words it is a new variety of flu which people are therefore unlikely to have much immunity to.