Jacobson v. Massachusetts is the seminal case regarding a state or municipality’s authority to institute a mandatory vaccination program as an exercise of its police powers. 8 In Jacobson, the Supreme Court upheld a Massachusetts law that gave municipal boards of health the authority to require the vaccination of persons over the age of 21 against smallpox, and determined that the vaccination program instituted in the city of Cambridge had “a real and substantial relation to the protection of the public health and safety.”9 In upholding the law, the Court noted that “the police power of a State must be held to embrace, at least, such reasonable regulations established directly by legislative enactment as will protect the public health and the public safety.”10 The Court added that such laws were within the full discretion of the state, and that federal powers