MONDAY, Jan. 19, 2015 (HealthDay News) -- Parents who refuse to have their children vaccinated appear to be clustered in certain areas, a new study suggests.
Among more than 150,000 children in 13 counties in Northern California, the researchers found five clusters where kids had missed one or more vaccinations by the time they were 3 years old.
"It's known from other studies that areas where there are clusters of vaccine refusal are at higher risk of epidemics, such as whooping cough epidemics," said lead investigator Dr. Tracy Lieu, a pediatrician and director of the division of research at Kaiser Permanente Northern California, in Oakland.
"Clusters may deserve special outreach efforts to make sure parents have all the information they need to make informed decisions about vaccination," she said.
Specifically, the researchers found the rate of missed vaccinations within these clusters ranged from 18 percent to 23 percent, compared with a rate of missed vaccinations outside the clusters of 11 percent.
Missed vaccinations for measles, mumps, rubella and varicella (chickenpox) were similar in all the clusters, they added.
In addition to missed vaccinations, children whose parents refused vaccinations were also found in clusters. In the clusters, vaccine refusal rates ranged from 5.5 percent to 13.5 percent, compared with 2.6 percent outside the clusters, Lieu's team found.
Parents who decline or delay vaccines do so for a variety of reasons, Lieu explained.
"Many parents have questions about the safety of vaccines, and it's natural to have these concerns even though there's reassuring evidence available about many questions regarding vaccine safety," she said.
"Sometimes parents decline vaccines they don't think are necessary; other studies have found this tends to happen with chickenpox vaccine, for example. Other times parents are concerned that vaccines might cause side effects," Lieu added.
The report was published online Jan. 19 and in the February print issue of the journal Pediatrics.
Dr. Paul Offit, a professor of pediatrics at Children's Hospital of Philadelphia, said there are two possible reasons people don't have their children vaccinated: they choose not to; they don't have good access to medical care.
"The most common reason people don't get vaccinated is because they are making the choice not to get vaccinated," he said.
Offit said parents who refuse to have their children vaccinated are usually white, upper middle class, college-educated and have a job where they have some measure of control.
"This is a person who believes that they can go on the Internet and know as much about vaccines as anyone who is giving them advice," he said. "These people believe, falsely, that vaccines cause diseases they don't cause -- autism, allergies, attention-deficit disorder and mental delays," he said.
In addition to parts of California, areas in Colorado, Michigan, Vermont and Washington state have clusters of unvaccinated children, noted Offit, who was not involved with the new study.
"The problem is the choice they are making is not for them, it's for their children," he said. "It's the children who are suffering from their parents' ignorance."
The U.S. Centers for Disease Control and Prevention's immunization schedule recommends a minimum of 17 separate shots during a child's first two years of life, including for hepatitis A and B, diphtheria, tetanus, pertussis (whooping cough), influenza, polio, measles, mumps, rubella and pneumococcal virus.
If you choose not to have your child vaccinated, you put your child at risk for these diseases and these diseases aren't trivial, Offit said. For example, 600 cases of measles were reported last year in the United States and cases are already being seen this year. "If you get to a few thousand cases, you will see children start to die of measles," he said.
Visit the U.S. National Library of Medicine for more on childhood vaccines.