JOHN K. BUSH, Circuit Judge. During the COVID-19 pandemic, Michigan State University (MSU) required its employees to receive a vaccine against the disease. Plaintiffs, who are MSU employees, objected. They claimed their naturally acquired immunity to COVID-19 should exempt them from the vaccine policy. That reasoning did not persuade MSU, which imposed disciplinary action against them for not getting vaccinated. The complaint below alleged that MSU violated plaintiffs’ constitutional rights and that the university’s vaccine mandate was preempted by federal law. The district court granted the university’s motion to dismiss. We agree with the district court that, as alleged, the university’s vaccine policy neither violated plaintiffs’ constitutional rights nor was preempted by federal law. We therefore AFFIRM.