Influenza is an infectious disease caused by a virus.

See also Map 105 Pneumonia.

Here is a map of extremes: in much of the country you are either twice as likely, or half as likely, as the average to meet your death with the assistance of this virus. It is not just in Scotland, particularly its northerly environs, that rates are especially elevated. Little pockets of extremes appear in parts of Norwich and Swindon, Blackpool and even in one of the more salubrious quarters of Oxford.

The disease itself being infectious will have tended to have killed in geographical clumps, but those who sign death certificates have a problem. Usually no virus is actually identified, so although influenza may have been present many doctors record the death as due to pneumonia.

The symptoms of influenza are chills, fever, sore throat, muscle pains, headache, coughing and general weakness. It is often confused with the common cold but influenza is much more severe.

Outbreaks of influenza occur in seasonal epidemics; in pandemic years it can kill millions of people. The 1918–19 pandemic is estimated to have claimed 40–50 million lives worldwide. Vaccines are now available but as the virus changes rapidly over time a vaccine that is formulated in one year may be ineffective the next.