The founder of Shake Shack, Danny Meyer, said his Union Square Hospitality Group will require indoor diners and drinkers at its restaurants to show that they’ve been vaccinated against COVID-19. Employees will also have to get the vaccine, Meyer said, although he didn’t say whether they would be fired or be forced to wear masks. However, the policy will not be extended to Shake Shack, a hamburger fast-food restaurant that has a number of locations in the northeastern United States. The policy will be implemented at the Union Square Hospitality Group, which oversees Gramercy Tavern, Manhatta, and Union Square Cafe....