Stanford Health Policy's David Studdert and Michelle Mello discuss SB 277, a new California law that ends exceptions to vaccination mandates based on religious and philosophical beliefs, leaving only medical exemptions as a path to avoid the vaccinations children are required to have before entering school.  Their report highlights the factors that lead to the law's passage, potential legal and enforcement challenges the law may face, and the possibility that this law may set a precedent for similar laws in other states.