Spanish influenza
Spanish influenza was a dangerous type of flu that was pandemic on Earth from 1918 to 1919. (PROSE: Casualties of War) Hugh Curbishley claimed to have been confined to a wheelchair as a result of "that flu epidemic back in '18"; he had in fact lied as he feared that his wife was going to leave him. (TV: The Unicorn and the Wasp)
In 1965, Venessa compared a strain of Indonesian flu she was negotiating an antivirus for to this outbreak. (TV: Children of Earth: Day Four)
By Christmas Eve 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)