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(CNN) — The rash of measles cases across the country has affected some states more than others. And, not surprisingly, the rules for vaccinating vary wildly from coast to coast.
Take California, for example, where more than 90 people have already been infected with measles this year. As in many states, parents in California don't have to vaccinate their children before kindergarten if they claim a religious or philosophical exemption.
Then there's Mississippi, which allows parents to opt out of vaccines only for medical reasons — no other exceptions. That state has a 99.7 percent vaccination rate — and not a single case of measles this year.
An array of exemptions
Every state requires vaccinations, and every state also allows exemptions for medical reasons, such as if a child has a weakened immune system.
That's where the consensus ends.
In many states, parents have two other ways they can avoid vaccinating children: religious and philosophical reasons.
The vast majority of the country — 48 states — allows religious exemptions, according to the National Conference of State Legislatures.
And 20 of those states also allow philosophical exemptions "for those who object to immunizations because of personal, moral or other beliefs."
The two states with the strictest vaccine requirements? Mississippi and West Virginia, which don't allow religious or philosophical exemptions.
The afflicted states
California, the epicenter of the current outbreak, allows exemptions for medical reasons and "personal beliefs." And parents have been using them.
During the last school year, 3.3 percent of California kindergartners — about 18,200 — were allowed to skip vaccinations, according to the Centers for Disease Control and Prevention. The vast majority of exemptions were due to personal beliefs.
"Schools should maintain an up-to-date list of pupils with exemptions, so they can be excluded quickly if an outbreak occurs," the California Department of Public Health said.
SALT LAKE CITY — With the recent cases of measles in the U.S., there has been momentum building behind the idea of perusing legal action against parents who choose not to vaccinate their children.
If that momentum continues, University of Utah Law Professor Teneille Brown said it could prompt the first legal case of its kind.
"It's a private suit, so there are no criminal sanctions. So nobody's going to jail. But it would be a judge who would decide that you had a duty to vaccinate your children. Or even if you spoke more generically, you had a duty to be more careful about the risk of infection to other kids," Brown said.
Brown said certain parameters would be required to build a viable legal case.
First, the affected party would have to show the choice not to vaccinate caused harm, including psychological reasons or loss of wages from work.
"The damages would be your child gets really sick from measles maybe goes blind or gets pneumonia or even dies," Brown said.
Second, the legal claim must show negligence -– or in legal terms, duty and breach negligence.
"The right judge, if this case came up before them would say, 'I'm willing to say there's a duty to do things that aren't careless and affect other people.' And I think not vaccinating your children could easily fit within that," Brown said.
Brown noted that these two parts would be relatively easy to claim in order to pursue legal action, but the third part of a lawsuit — proving cause — would be one of the major challenges in a case like this.
"That you didn't vaccinate your child and it caused injury to my child, but you'd need to show the causation part, and I think that's where it could be tricky — to pinpoint the exact person who infected your child," Brown said.
In order to prove who did it, Brown said people would have to investigate a timeline of where likely infections possibly took place. And with more than 100 measles cases in 14 states, according to the CDC, that could become especially challenging.
But the other side, Brown said the federal government will compensate families whose kids suffered adverse reactions to the vaccine for measles and other diseases. She said this route is easier for both parties, rather than in trying to bring a malpractice suit against doctors or hospitals.
But the number of measles cases in California over the past month — 92 — is higher than the median number of cases for the entire country for each year between 2001 and 2011, according to CDC figures.
Arizona is the next hardest-hit state, with at least seven measles cases already this year. Nearly 5 percent of Arizona kindergartners were able to skip vaccinations last school year due to medical reasons or, more commonly, their parents' personal beliefs.
New York and Utah each has at least three measles cases this year. New York allows religious exemptions, but not philosophical ones; Utah allows both.
Overall, about 94.7 percent of kindergartners across the country last year were vaccinated against measles, according to the CDC.
Mississippi and West Virginia, the two states that allow only medical exemptions to vaccination, have had no measles cases this year.
An incredibly contagious disease
Before the measles vaccine was introduced in the 1960s, many children came down with the disease by age 15. About 3 million to 4 million people got measles each year in the United States. Among them, about 500 people a year died, and 4,000 developed encephalitis, or brain swelling.
Since then, the disease has largely disappeared in the United States. But international travel has spurred sporadic outbreaks in recent years.
Many of the recent measles victims are part of "a large, ongoing multi-state outbreak" linked to Disneyland in California, the CDC said.
The disease is extremely contagious for several reasons:
• An infected person can spread it four days before developing a rash.
• 90 precent of people who are not immune and are close to someone with measles will also get infected.
• The virus is airborne.
• It can also live on infected surfaces for up to two hours.
Most, but not all, doctors agree
The overwhelming sentiment from the medical community is that the measles vaccine is safe and effective. But Arizona cardiologist Dr. Jack Wolfson is a rare voice of dissent.
"It's a very unfortunate thing that people die, but unfortunately people die," Wolfson said. "And I'm not going to put my child at risk to save another child."
Those words struck a nerve with Dr. Tim Jacks, a pediatrician whose own daughter has leukemia and, therefore, a weakened immune system.
"I can definitely, wholeheartedly say that the medical community, the medical literature does not support the statements he makes," Jacks told CNN's Anderson Cooper.
"The question I might have for him is, if you were in my situation, and your two children — who you're doing your best to protect — if they were suddenly exposed to measles, what would your thoughts be at that point?"
CNN's Elizabeth Cohen contributed to this report.
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