How movement spread COVID-19

A recent study found countries with certain international travel restrictions have suffered fewer COVID-19 deaths.

Why it matters: Before the novel coronavirus, most experts believed border closures weren't effective in slowing the spread of a pandemic. But it's become clear that addressing how people move is key to controlling a disease, even if closures come with serious costs.

What's happening: Researchers in Germany studied the effect of entry bans and mandatory quarantines on COVID-19 mortality, and found the earlier such measures were implemented, the greater the effect they had on limiting deaths.

• Countries that put in place travel restrictions in early March had morality rates 62% less than countries that implemented them after mid-March, or not at all.

Of note: The study found mandatory quarantines for incoming travelers were more effective than outright entry bans, largely because such bans often exempted citizens and permanent residents, while quarantines usually applied to everyone.

• That was the case with the U.S. ban on travel from China, which was applied a month after China first reported COVID-19 outbreaks and which exempted citizens and permanent residents.
• The U.S. lost track of at least 1,600 people flying in from China in just the first few days after the ban went into effect, according to reporting from the AP.
• Border controls are of little use if governments don't track and quarantine travelers coming from infected areas.

Between the lines: Travel within a country — which is much harder to restrict than international movement — clearly spread the virus as well.

• A recent paper from researchers at New York University found "urban flight" — people fleeing large cities that hosted some of the first major outbreaks of the novel coronavirus — led to greater COVID-19 case growth in the regions they arrived in.

The bottom line: A virus only moves with its host. One lesson we should learn for future pandemics is that restricting that movement is key to controlling a new pathogen, even though the costs of such controls will only grow in a globalized world.