The opening title sequence depicting the germ being transferred from China via air travel all around the world is often referred to as one of the most memorable and frightening titles ever made for television.
Creator Terry Nation left after the first series because of differences with producer Terence Dudley.
Carolyn Seymour was dropped after the first series due to a difficult relationship with producer Terence Dudley.
Ian McCulloch was cast as Peter West in the Italian horror movie L'Enfer des zombies (1979) on the strength of his performance in this series, which was a huge hit in Italy, where it was known as "I Sopravvissuti".