Want to end state lockdowns? Send in the coronavirus detectives.

To end coronavirus lockdowns, states will need a robust network of human contact tracers. Massachusetts shows how that process can start.

As American states mull the easing of COVID-19 social restrictions, many are turning to a trusted tool for controlling infectious diseases: contact tracing.

Known as “disease detectives,” contact tracers are people who work to halt the spread of a virus. They reach out to individuals who are confirmed cases and then trace others the person came into contact with, from family members to subway riders. It’s a hands-on containment...