Is Contact Tracing Hopeless in the United States?

How to do contact tracing when someone’s contacts may be thousands of strangers

A French mobile phone application StopCovid, developed to trace people who test positive for Covid-19. Credit: Chesnot / Getty Images

If you look at the countries that successfully flattened the curve and are working on reopening — like South Korea and New Zealand — they all have something in common: contact tracing.