Boom’s vaccine mandate is among only a handful issued by health-care institutions in America. While more than 380 colleges and universities, generally in blue states, and a few travel companies have imposed vaccine mandates, most other employers have held back, worried about the difficult politics surrounding the coronavirus vaccines and the untested legal issues involving vaccines cleared under the Food and Drug Administration’s emergency authority. Boom’s mandate worked — more than 98 percent of the hospital’s 26,000 employees are now vaccinated ahead of a June 7 deadline, including more than 3,000 who got the shots after Boom’s call to action. But the hospital chain fired its director of corporate risk and insurance for refusing to get inoculated, and it is now facing a broader backlash. Several employees are vowing to skip the shot, rallying around Jennifer Bridges, a nurse who has worked in the hospital’s coronavirus unit and who is threatening to sue. Bridges says she’s willingly submitted to “every vaccine known to man,” but believes the coronavirus vaccines need further study.