Common cold

The common cold was an illness caused by a virus. It was frequently contracted by humans.

Henry van Statten found the cure for the common cold in a crater. However, he chose not to market it as he could make more money from repeatedly selling duds. (DW: Dalek)

Dodo Chaplet nearly wiped out the inhabitants of the Ark when she passed it onto them, as they had no immunity to the infection. A Monoid died from the virus. The First Doctor was able to develop a cure and save the ill. He used Steven Taylor as a guinea pig for his tests on the orders of the Ark's commander.

However, the Doctor cured but one strain. After he and his companions left, the cold severely weakened the human population of the Ark. (DW: The Ark)