After walking on the moon in 1969, the Apollo 11 crew spent 21 days sealed in a modified Airstream trailer in case they had carried back a lunar microbe. This episode traces quarantine from that trailer back through history, starting with the difference between isolating the sick and restricting people who might have been exposed. It covers seven day isolation rules in Leviticus, Ibn Sina’s Canon of Medicine in 1025, Ragusa’s 30 day rule for arriving ships in 1377, and Venice’s 1448 extension to 40 days, the quarantena, which happened to cover the plague’s roughly 37 day course.

The story moves to the village of Eyam, which sealed itself off in 1665 and lost at least 260 people, and to 1918, when American Samoa’s blockade kept flu deaths at zero while neighboring Western Samoa lost over 20 percent of its adults. It explains maritime yellow flags, the 1852 sanitary conventions, Mary Mallon’s 26 years in isolation, the 1984 Siracusa Principles, and nurse Kaci Hickox’s 2014 challenge to an Ebola quarantine. A Lancet review documents the psychological toll.

• The cordon sanitaire and why it works as a geographic quarantine
• Governor John Martin Poyer’s total blockade and the political will it required
• Why a single yellow Quebec flag now means a ship is healthy
• Mary Mallon, linked to at least 53 typhoid cases and three deaths, who never showed symptoms
• Proportionality and the least restrictive means test in modern quarantine law