Over the past decade, it has become easier for parents to exempt their children from vaccination requirements. It’s no coincidence that it also has become easier to catch a preventable disease.

Scientists have long stressed the importance of vaccines in public health, but a study released this summer provides the most rigorous overview to date about what rules and regulations promote the highest immunization rates and how those rates thwart outbreaks. The study’s review of individual policies gives local legislators a toolbox for building effective vaccination laws.

The Health Affairs report, conducted by health policy experts at the University of Georgia, lends additional legitimacy to a view most sensible people already hold — that vaccines, and the laws that enforce them, save lives.

According to the study, the states with the weakest rules and lowest rates experience the highest incidence of preventable diseases such as measles and whooping cough. Tough laws, on the other hand, lead to more vaccinations and less illness. This confirms what health officials have said for decades, yet the study also does something new and useful: It untangles the web of state vaccine policies and measures exactly what effect each component of each law has on rate reduction.

What policies work best? Some are obvious. Banning philosophical exemptions, whereby parents can claim that their personal, but not necessarily religious, views bar them from allowing their children to be immunized, raises vaccination rates by 0.1 percent.

Others are subtler, smaller tweaks that can have a surprisingly large impact. Requiring a state health department official to sign off on a nonmedical exemption, for example, pushes immunization rates up 1.12 percent. This modest change helps guarantee that the quickest and easiest route to enrolling a child in school is to get him or her vaccinated — not to fill out and file an exemption form. But only four states have the policy in place.

From 2002 to 2012, the study shows, the occurrence of whooping cough was twice as high in states with the loosest laws as in states with the strictest laws. That is no surprise, when too-low levels of vaccination threaten the collective immunity that keeps infants and sick people safe. But legislators should take note that even a percentage-point decrease in the vaccination rate can transform a community into a breeding ground for disease for children and the infirm. It is up to these lawmakers to enact policies ensuring a healthful environment.

In many ways, the study’s authors have completed the bulk of the lawmakers’ work for them. Now, they just have to do the right thing.

Editorial by The Washington Post