Influenza is a respiratory infection caused by the influenza virus. The secondary diseases associated with influenza include ear infections and pneumonia, which can require hospital care and can even lead to death. Deaths resulting from an influenza infection are normally caused by either a bacteria infection that develops as a secondary disease or by the worsening of an underlying condition.
There are four main types of influenza viruses: A, B, C and D. The A and B types are the cause of annual influenza epidemics among the population. In Finland, seasonal influenza epidemics usually occur between November and April. The peak for seasonal influenza cases is normally reached in February or March. An influenza epidemic can spread and become a worldwide pandemic.
The best protection against influenza is vaccination. Influenza can also be treated and prevented using antiviral drugs.