The parent of a child who caught measles from a purposefully unvaccinated child could sue, but it would be hard to win, George Annas, who chairs the department of health law and bioethics at Boston University, said.
"I think you could make an argument that you have a moral responsibility, but it would be extremely difficult to argue this as a tort case," he said.
"As long as you're following state law, it's almost inconceivable that any court would say you're responsible for something that has been sanctioned by your state."
Both cause and duty would be most difficult to prove, she said. The measles is so contagious -- spreading to an average of 18 people for every one infected person -- that it would be hard to say who got the virus from whom.
Also, Annas said, the parents of the child too young or unable to get the measles vaccine for medical reasons may have more of a duty to keep their child away from unvaccinated children, putting some of the blame on them.
Rosenbaum said, "It doesn't work because once you allow individuals to make choices on all sides -- whether to immunize or not immunize, take your child to school or not -- you get into the murky world of tort litigation."That's why this issue is really a public health issue."
But bioethicist Arthur Caplan of the NYU Langone Medical Center in Manhattan said parents who choose not to vaccinate their children should be held responsible for the consequences of their actions.
"Even if the government says you can opt out, if a kid who's got the measles brings it to a day care center and sickens or kills my newborn baby, of course I have the right to sue you, and I should," Caplan said.
He likened the situation to an accidental gun death. If a person has the right to own a gun and leaves it on a table, and a neighboring child picks it up and shoots himself, Caplan said, the gun owner is responsible for what happened.