Investigators aren’t casting a wide enough net to catch Covid-19 cases before they spread

PARISWhen countries across the West emerged from lockdown in the spring, governments trained legions of investigators to identify and isolate people potentially infected with the coronavirus. The goal was to prevent a resurgence of the pathogen.
Four months later, the systems to find people who might pass on infections, known as contact tracing, are in disarray. Europe and the U.S. are each recording tens of thousands of new daily infections.
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