People around the world are currently isolating themselves or in a formal quarantine to prevent the spread of the SARS-CoV-2 coronavirus. But for decades, astronauts have been quarantined to ensure that they were virus-free and ready to fly (or, in the case of Apollo, to make sure they didn’t bring home any “moon bugs.”)

This quarantine period “ensures that they aren’t sick or incubating an illness when they get to the space station,” NASA spokesperson Brandi Dean told Space.com.