Influenza

Influenza, often shortened to the flu, was a type of Earth virus. Some strains of the disease were known to be particularly deadly.

Missy believed that influenza was just a "cold dressed up in a nice frock," but Bill Potts informed her that it was particularly dangerous for the elderly and children and could develop into pneumonia. (PROSE: Pain Management)

Symptoms
The disease's symptoms could include delirium, diarrhoea, and vomiting, similar to those of a growth stage experienced by Killorans around the age of four. (PROSE: Mentioning the War)

History
Circa 1862, a twelve year old Gwyneth lost both her parents to the disease. (TV: The Unquiet Dead)

In 1906, Lady Edith Greystone died of influenza. (PROSE: 64 Carlysle Street)

In 1918 through 1919, an outbreak of Spanish flu killed around five percent of the human population worldwide, more than World War I. (PROSE: The Clockwise Man, TV: Children of Earth: Day Four) It's possible the Dark Forces' dissipation was the cause of the outbreak. (PROSE: Casualties of War) Hugh Curbishley claimed that he had become restricted to a wheelchair as a result of the 1918 epidemic. (TV: The Unicorn and the Wasp)

As a sailor, Ben Jackson once saw a stowaway who had died of the disease before being discovered by the ship's crew. (PROSE: Pluto)

In 1965, in exchange for twelve children, the 456 provided an antivirus for a brand new form of the Indonesian flu which would mutate into a deadlier form within four months and stood to wipe out 25 million of Earth's human population if unchecked. (TV: Children of Earth: Day Four)

In the 2000s, the alien virus carried by the toy Cuddlesomes was reported as a flu outbreak. Some believed it was specifically H591 Avian flu and Miranda Evenden suggested it came from toy factories in Asia. (AUDIO: Cuddlesome)

Mickey Smith once suffered from the flu and was nursed back to health by Rose Tyler. (PROSE: The Stone Rose)

A poster was present in Albion Hospital by at least March 2006 that had a yellow background and text reading "Don't fall down with Flu", with the word "Flu" stylised in red, and humanoid patterns in red, purple, yellow, blue, and green below it. It was located next to a poster regarding the NHS. (TV: Aliens of London)

In late 2006 or early 2007, three months before the destruction of Deffry Vale High School, half of the staff became sick with the flu following the arrival of the new headmaster. (TV: School Reunion)

In December of 2007, Wilfred Mott was unable to attend his granddaughter's wedding to Lance Bennett because he was bedridden with a severe infection which his daughter referred to as "Spanish flu". (TV: The Sontaran Stratagem)

In the 2010s, the Twelfth Doctor hypnotised Atif Basra, the caretaker of Coal Hill School, into believing he had the flu. (TV: The Caretaker)

The Twelfth Doctor claimed regeneration for Time Lords was like "man flu". (TV: Hell Bent)