If it is a very bad year, this may amount to what is called an epidemic. How much flu there will be each year is difficult to predict. For most people, flu is a nasty experience. For some people flu can lead to more serious illnesses such as bronchitis and pneumonia which may require treatment in hospital. Sadly, every winter a lot of mainly older people die from influenza.
Flu vaccines contain the ingredients from three different strains of flu virus.
The viruses are grown in hens' eggs, then killed and purified before being made into vaccine. About a week to ten days after the vaccine is injected, your body makes antibodies to the vaccine viruses. These antibodies help to protect you against any similar viruses you then come into contact with. This protection lasts for about a year. Flu vaccinations are pretty effective.