“Nonetheless, the difficulty here—at least for present purposes—is that this case involves both a set of high-level judgments by MGB (that is, whether to require vaccinations generally, whether to permit exemptions under certain circumstances, and if so, according to what procedures) and a series of separate low-level individual judgments (that is, whether a particular employee qualified for a particular exemption),” U.S. District Chief Judge F. Dennis Saylor IV wrote.