Overnight Health Care: DC, New York require health care workers to get vaccinated | How the delta variant took over the US | Dallas school district keeps mask mandate despite court ruling

Welcome to Monday’s Overnight Health Care. The anonymous messaging app Yik Yak is back after a four-year hiatus – just as college students are returning to campus. If you have any tips, email us at nweixel@thehill.com, psullivan@thehill….