State and local health departments have been hiring and training contact tracing workers to help contain Covid-19 outbreaks. But the US is still far behind its economic peers in ramping up these capabilities. | Jahi Chikwendiu/The Washington Post via Getty Images

Why is the US so bad at tracing Covid-19 contacts?

Three words explain why many developed countries have contained their coronavirus outbreaks more successfully than the United States: test, trace, and isolate.

The most effective containment strategy involves testing enough people to identify new cases, tracing all of their potential contacts, and isolating the people who may have been exposed before they can spread the virus to anybody else. But today, six months into the pandemic, America is still struggling to stand up these basic features of an effective public health response.

In the states where infections have exploded in the last