Spanish influenza was a dangerous type of flu that was pandemic on Earth from 1918 to 1919. (PROSE: Casualties of War)
In 1965, Venessa compared a strain of Indonesian flu she was negotiating an antivirus for to this outbreak. (TV: Children of Earth: Day Four)
In 2007, Wilfred Mott was unable to attend his granddaughter's aborted wedding to Lance Bennett after falling ill with a non-lethal strain of Spanish flu. (TV: The Runaway Bride, The Sontaran Stratagem)