The Exemption Is the Policy

There is no national childhood vaccination law in the United States. There is a recommended schedule, and there are fifty sets of rules about who may attend school.

The federal summary of state requirements is a table rather than a regulation. The federal government advises; the states legislate; school districts administer.

Every state requires some vaccinations for school entry, and every state allows exemptions from them. The arguments in public are almost always about the requirement. The number that decides whether a disease spreads is the exemption.

The 1905 decision is the reason the requirement side of that equation is settled. In Jacobson v. Massachusetts the Supreme Court upheld a local smallpox vaccination mandate, holding that a state's police power extends to reasonable measures to protect public health.

That case is more than a century old and is still the foundation. It has never been the contested part of American vaccination policy.

The contested part is who gets to opt out, and on what basis. Every state permits medical exemptions, for children whose health makes a vaccine unsafe. Most permit religious exemptions. Some permit philosophical or personal-belief exemptions, which require no stated ground at all.

One state's exemption rule shows the machinery in a single jurisdiction: what a parent must present, to whom, and what the school must then do.

Those three categories look like variations on a theme. They produce very different results, because they impose very different costs on the parent.

A medical exemption requires a clinician's judgment. A religious exemption usually requires a signed statement. A personal-belief exemption often requires only a form.

Coverage follows the cost of opting out, not the strength of the requirement. Two states with identical mandates and different exemption procedures will have different vaccination rates, and the gap will grow in the communities where opting out becomes normal.

That is why the framing matters so much. A debate conducted about whether vaccines should be required is a debate about a settled question, and it distracts from the live one.

The coverage survey is where the live question shows up. It reports kindergarten vaccination coverage and exemption rates by state, year after year, and it is the closest thing the country has to an early warning system.

Measles is the disease that finds any gap first. It is among the most contagious infections known, and the threshold for stopping it spreading is unusually high — about 95 percent of a community immune.

A statewide average above that threshold can conceal a school district well below it, and the virus does not encounter averages. It encounters classrooms.

This is the part of the argument that gets lost when the question is put as personal freedom against state power. Vaccination is one of the few medical decisions whose benefit is partly collective: a vaccinated child protects the infant too young to be vaccinated and the classmate whose leukaemia treatment makes the vaccine unsafe.

Those two children are the people a medical exemption exists to protect, and they are the people a large number of non-medical exemptions puts at risk.

None of which tells a legislature what to do. Exemption policy is a genuine political choice, and states have made different ones for a century.

It does say where the choice is being made. Not in Washington, not in a court that decided the question in 1905, and not in the sentence that says vaccines are required. It is made in the paragraph that says how a parent may decline, and how hard that paragraph is to use.

An exemption rate is also the rarest thing in this argument: a number that is published, comparable across states and updated every year.

Anyone who wants to know whether a state's policy is working does not need a philosophical position on mandates. They need last year's figure and this year's, for the district rather than the state.