More parents say no to vaccines, endangering kids

More parents are opting not to have children vaccinated with all the shots health officials recommend, endangering their kids and fostering disease outbreaks, a study said.

While all states require schoolchildren to be vaccinated, 21 allow parents to exempt their own kids for personal reasons. Clusters of unvaccinated children are growing in these states, leading to outbreaks of measles and pertussis, or whooping cough, according to the analysis published in the latest New England Journal of Medicine.

The number of mandated vaccinations has increased in recent years so children now get as many as 33 inoculations, most of them shots, to prevent 15 diseases, said Lance Rodewald, immunization director of the U.S. Centers for Disease Control and Prevention in Atlanta. While routine coverage has never been higher nationally, the local clusters of unvaccinated youngsters are a mounting concern, he said.

"Infectious diseases are transmitted at the local level," said Saad Omer, an epidemiologist at the Rollins School of Public Health at Emory University in Atlanta, and the lead author of the study. "We have shown that vaccine refusals cluster geographically and that there's an association between those clusters and outbreaks of pertussis."

The number of vaccinations recommended by the CDC has increased by nine for boys and 12 for girls since 2000, not including the annual flu shots health officials added to the list last year, Rodewald said. Most states don't require children to get flu shots to attend school.

Some parents worry about the risk of side effects and believe that mercury, previously used as a vaccine preservative, is linked to rising rates of autism, the study noted. There's no evidence to support that concern, Omer said.

The FDA has been working with vaccine manufacturers for at least a decade to reduce or eliminate mercury. The preservative is now used only in some influenza vaccines, where it is found in trace amounts, said Tom Skinner, a spokesman for the CDC.

Omer and his colleagues at Johns Hopkins Bloomberg School of Public Health and the National Vaccine Program Office of the U.S. Department of Health and Human Services reviewed studies looking at vaccination exemptions and rates of infection.

All states permit medical exemptions and 48 allow them for religious reasons, according to the study. In states that grant only these types of exemptions, the rate of unvaccinated children remained at 1 percent from 1991 to 2004.

In the 21 states that let parents excuse their children from shots for personal reasons, the average number of parents seeking exemptions increased to 2.5 percent in 2004 from 1 percent in 1991, Omer said. In some local areas, the numbers are far higher, he said.

"That's just the tip of the iceberg," he said.

From January 1 to April 25, 2008, five measles outbreaks struck the U.S., infecting 64 people, according to the paper. All but one were unvaccinated or had no evidence of inoculation. In Colorado, children who were exempted from vaccination were 22 times as likely to get measles as those who got the shots, Omer and his colleagues found.

High vaccination rates also protect the few people that don't get shots by reducing the number of people who can transmit a disease and keeping certain germs from circulating, Rodewald said. This kind of protection, known as herd immunity, can decline when the number of people who don't get vaccinated rises, he said.

"Endemic measles has been eliminated in the U.S.," said Rodewald. "So if a child is not vaccinated over here, they won't get measles because they won't be exposed to it. But if they leave the U.S. and go to a place where measles exist, they could catch it and then bring it back and serve as a transmission point to other children who aren't vaccinated."

That is exactly what happened last year when an unvaccinated child went to Switzerland, contracted measles and brought it back to the U.S., Rodewald said.

Since Massachusetts first required smallpox inoculations in 1809, public support for vaccinations has gained steadily, with occasional periods of greater opposition.

"It happens in cycles," Omer said. "If vaccination rates fall to a relatively lower level, we'll start seeing outbreaks. Then there's a backlash on the other side and the rate goes up again."