In several major cities, public health officials work every year to monitor the flu. It's called sentinel surveillance. And as early as mid-February, the government had a plan to use that system to find early cases of the coronavirus, by testing patients with flu-like symptoms. But NPR's Lauren Sommer reports the effort was slow to get started, costing weeks in the fight to control the spread of the virus. Read more from Lauren's reporting here. Email the show at shortwave@npr.org.