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- Season 0 1966-12-25
- Season 1 1964-02-04
- Season 2 1965-01-06
- Season 3 1966-01-02
- Season 4 1967-01-17
- Season 5 1968-01-02
- Season 6 1969-01-02
- Season 7 1970-01-05
- Season 8 1971-01-04
- Season 9 1972-01-03
- Season 10 1973-01-04
- Season 11 1974-01-07
- Season 12 1975-01-20
- Season 13 1976-01-05
- Season 14 1977-01-07
- Season 15 1978-01-06
- Season 16 1979-02-26
- Season 17 1980-01-14
- Season 18 1981-01-05
- Season 19 1982-01-11
- Season 20 1983-01-10
- Season 21 1984-01-09
- Season 22 1985-01-07
- Season 23 1986-01-06
- Season 24 1987-01-05
- Season 25 1988-01-04
- Season 26 1989-01-09
- Season 27 1990-01-08
- Season 28 1991-01-07
- Season 29 1992-01-06
- Season 30 1993-01-04
- Season 31 1994-01-10
- Season 32 1995-01-09
- Season 33 1996-01-08
- Season 34 1997-02-27
- Season 35 1998-02-19
- Season 36 1999-01-28
- Season 37 2000-01-12
- Season 38 2001-01-25
- Season 39 2002-01-10
- Season 40 2003-01-09
- Season 41 2004-01-08
- Season 42 2005-01-13
- Season 43 2006-01-12
- Season 44 2007-03-13
- Season 45 2008-01-15
- Season 46 2009-01-26
- Season 47 2009-10-13
- Season 48 2010-09-27
- Season 49 2011-08-08
- Season 50 2012-07-23
- Season 51 2013-08-12
- Season 52 2014-08-18
- Season 53 2016-03-16
- Season 54 2017-01-19
- Season 55 2018-02-05
- Season 56 2019-01-23
- Season 57 2020-01-16
- Season 58 2021-01-04
- Season 59 2022-03-31
- Season 60 2024-07-22
Season 60 Episode
- Season 17 The Ghost Of The Amoco Cadiz
- Season 17 You Are Old, Father William
- Season 17 Cleared for Take-Off
- Season 17 A Sporting Chance
- Season 17 The Cancer Detectives of Lin Xian
- Season 17 The Big If...
- Season 17 Cash from Trash
- Season 17 Encounter with Jupiter
- Season 17 Portrait of a Poison
- Season 17 Magnet Earth
- Season 17 Goodbye Gutenberg
- Season 17 Invasion of the Virions
- Season 17 Beyond the Milky Way
- Season 17 Little Boxes
- Season 17 The Other Kenya
- Season 17 Moving Still
- Season 17 The Way Out
- Season 17 The Dead Sea Lives
- Season 17 Once in a Million Years
- Season 17 Smoker's Luck
- Season 17 Behind the Horoscope
- Season 17 The Mondragon Experiment
- Season 17 The Spike
- Season 17 The Slatemakers
- Season 17 Anatomy of a Volcano
Horizon - Season 17 Episode 12 Invasion of the Virions
7.40 60 minutes Investigates various virus infections ranging from smallpox and rabies down to influenza and the common cold. The way they function and the reasons the body builds up resistance to some and not to others.
