As new and more contagious variants of the coronavirus have emerged in recent months, more nations are implementing mandatory quarantine facilities for entry. Canada and England announced last week that they will closely monitor arrivals in quarantine facilities to prevent new variants from gaining traction, following examples set by nations like New Zealand early in the pandemic.

Government-imposed quarantines have proved effective at detecting cases before they get into the country. They effectively halt travel for anyone unwilling to spend (and often pay for) a waiting period confined to a hotel room and monitored by health officials.

[U.S. arrivals will now have to quarantine. But officials haven’t said how they plan to enforce it.]

But not all government-imposed quarantines are equal, with varying surveillance levels, out-of-pocket costs and stay lengths that range from three days to three weeks.

Here are the quarantine requirements that have largely shuttered tourism in destinations around the world. ...