


Influenza spreads around the world in a yearly outbreak, resulting in about three to five million cases of severe illness and about 250,000 to 500,000 deaths. In the Northern and Southern parts of the world outbreaks occur mainly in winter while in areas around the equator outbreaks may occur at any time of the year. Death occurs mostly in the young, the old and those with other health problems. Larger outbreaks known as pandemics are less frequent. In the 20th century three influenza pandemics occurred: Spanish influenza in 1918, Asian influenza in 1958, and Hong Kong influenza in 1968, each resulting in more than a million deaths. The World Health Organization declared an outbreak of a new type of influenza A/H1N1 to be a pandemic in June of 2009. Influenza may also affect other animals, including pigs, horses and birds.


Frequent hand washing reduces the risk of infection because the virus is inactivated by soap. Wearing a surgical mask is also useful. Yearly vaccinations against influenza is recommended by the World Health Organization in those at high risk. The vaccine is usually effective against three or four types of influenza. It is usually well tolerated. A vaccine made for one year may be not be useful in the following year, since the virus evolves rapidly. Antiviral drugs such as the neuraminidase inhibitors oseltamivir among others have been used to treat influenza. Their benefits in those who are otherwise healthy do not appear to be greater than their risks. No benefit has been found in those with other health problems.