Lawsuits have not been widely employed so far; Reiss told me that, to her knowledge, no one has actually sued someone for infecting their child due to failure to vaccinate. But lawsuits do have some advantages.

Perhaps the biggest one is that they would be relatively simple to implement. Specific legislation authorizing lawsuits in these cases would make them easier to win, but such legislation isn't necessary, Reiss argues. It's true that many states offer exemptions for parents who don’t want to vaccinate their kids, but such exemptions don't necessarily rule out lawsuits. State legislatures didn't consider the issue of lawsuits when they created the exemptions, and "depriving a family who was harmed by another's negligence is a big deal, and deciding the legislature did it inadvertently is a big leap," Reiss told me. She added, "Actions can be legal but not reasonable. It's legal to have a stack of hay in your yard, but if it's a fire hazard and you start a fire, you may be liable … The fact that behavior is legal does not mean you're not negligent to engage in it—and if you're negligent and someone is hurt, in our system you usually have to pay."

There is good legal reason to believe that an injured party could bring and win a lawsuit for failure to vaccinate under current law, which means that lawsuits are an immediate solution, one that can be used now without waiting for the long, arduous process of creating new laws.

There are a number of barriers to a potential lawsuit. It may be difficult to prove that a given person infected another, for example. There's little provision for insurance against vaccination lawsuits, which means that the person sued may have little ability to pay. Still, Reiss says that these problems need not be crippling. Plaintiffs always have to prove cause—in a vaccine case you'd use science and evidence to make the best case, just as you would in any other suit. And if vaccine lawsuits became more common, insurance might adapt to address them. In any case, even though some plaintiffs might not be able to pay, Reiss thinks it’s still reasonable to allow complainants to sue the ones who can.

Perhaps the biggest problem with lawsuits as a policy solution, though, is that there's little reason to think that they'll actually address broader issues. A lawsuit might help one family obtain compensation, but it seems unlikely that lawsuits in general will push more people to vaccinate their children. In fact, there's some concern that lawsuits might make things worse, according to Ross D. Silverman, a professor in the Department of Health Policy and Management at Indiana University. Silverman told me he worried that lawsuits "undermine trust in the public-health system, probably won’t increase the number of people taking up vaccination, and create a dangerous precedent."