Unvaccinated people account for many cases of measles, whooping cough

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KANSAS CITY, Mo. -- Measles was declared eliminated in the U.S. 16 years ago, but in recent years, there have been hundreds of cases. Now researchers find a substantial proportion of measles and whooping cough cases is related to vaccine refusal by parents.

Chalon Davis is happy at a Children's Mercy clinic. The 13-month-old's cheerfulness will be briefly interrupted by four shots including the measles, mumps and rubella vaccine. His mom believes vaccination is the right thing to do.

"I really don't understand why parents don't do it," Victoria Davis said.

Researchers wondered how much of a role vaccine refusal has played in measles outbreaks in America since 2000. They found that more than half of people who got measles had no history of measles vaccination. And in three-quarters of those cases, parents intentionally didn't get their children vaccinated because of philosophical or religious reasons.

"They may pass it to other people that also have not had their immunizations and that's what we've seen," said Dr. Elizabeth Simpson, a pediatrician at Children's Mercy.

They may also pass it to those who've been immunized since no vaccine is 100 percent effective. It's why Dr. Simpson applauds California's decision last year to require immunization. It followed a measles outbreak that started at Disneyland. Missouri still allows both personal belief and religious exemptions while Kansas allows religious ones. Dr. Simpson says the new research strengthens the argument against those exemptions.

"I believe we need to require immunizations for all of our institutions -- our schools and our day cares." she said.

The new research also looked at whooping cough outbreaks and found vaccine refusal played a role in those, too, but there were several outbreaks in highly vaccinated populations. Researchers say that's the result of the whooping cough vaccine's effectiveness diminishing over time.

Dr. Simpson reminds parents that vaccines are the greatest public health tool, and benefits far exceed risks. The new research is in the Journal of the American Medical Association.