The 2015 measles outbreak continues to resonate. Last month, California became the third state to disallow vaccination exemptions for school entry based on religious and philosophical grounds, leaving only medical exemptions intact. Public-health advocates announced a victory, while families opposed to mandated vaccinations regrouped to continue the fight, claiming violation of certain constitutional rights.

Public-health law expert Wendy E. Parmet is the George J. and Kathleen Waters Matthews Distinguished Professor of Law and Professor of Public Policy and Urban Affairs at Northeastern University. She co-authored an article in the July 22 issue of the New England Journal of Medicine exploring the evolving landscape of vaccination policy. We asked her to discuss some of the implications of the new law in California.

Why do proponents argue that all children should have up-to-date vaccinations for measles, rubella, and other diseases before they can enter schools and child-care institutions?

The requirement that children be vaccinated before enrolling in school or day care is one of the most effective tools we have for preventing outbreaks of vaccine-preventable diseases such as measles. Children are especially susceptible to these diseases, which can spread quickly in a school or day care center when vaccination rates are low.

By requiring children to be vaccinated, we can foster “herd immunity,” which occurs when there aren’t enough people susceptible to a disease for it to spread in the community. Herd immunity protects children and adults who cannot be vaccinated or for whom vaccines fail to provide immunity.

What are the constitutional issues that come into play in the debate about vaccination mandates?

Opponents of vaccination have raised several constitutional claims. They have said vaccination requirements violate the due-process clause of the 14th Amendment, the equal-protection clause of that amendment, and the right to free exercise of religion as protected by the First Amendment.Challengers have also claimed that vaccination requirements violate the right to education, which is recognized in many states.

Overwhelmingly, the courts have rejected such claims, except in unusual and limited circumstances. In the leading 1905 case, Jacobson v. Massachusetts, the Supreme Court of the United States affirmed a Massachusetts law mandating that all residents be vaccinated against smallpox during an epidemic.

Less than 20 years later, in Zucht v. King, the Supreme Court rejected a challenge to a Texas law requiring that children be vaccinated before entering school. In the almost 100 years since Zucht, the courts have not changed their tune. Just last winter the United States Court of Appeals for the Second Circuit rejected due process, equal protection, and First Amendment challenges to New York’s school vaccination law.

Why do you suggest in the NEJM article that states task health departments, rather than school administrators, with overseeing compliance with vaccination law?

School administrators are educators, not health officials. Requiring them to enforce vaccine laws puts them in an adversarial relationship with parents. This can undermine parents’ trust in their children’s schools.