Eighteen state legislatures, including California's, have considered exemptions to immunization mandates in the last several years — and the issue remains a topic of debate, researchers said Tuesday.
Most of the bills introduced in those 18 states sought to expand the exemptions available to school immunization requirements, but none of those bills passed, researchers wrote in the Journal of the American Medical Assn.
In California, a bill signed into law in 2012 allows parents to send their children to public school without vaccinations after they submit a form signed by a health professional affirming that they had been informed about the risks and benefits of immunization.
Requirements that children going to school receive certain vaccinations "have played an important role in maintaining high immunization coverage in the United States," the researchers, led by Saad Omer of Emory University, wrote.
Those mandates set out exemptions for reasons such as religious beliefs or medical conditions. The easier exemptions are to claim, the researchers wrote, the higher the rate of their use and the higher the "disease risk among exemptors themselves and in the communities in which they reside."
The researchers looked at the 36 bills introduced from 2009 through 2012 by state, by whether the state allowed a "personal belief" exemption, and by whether the parent seeking such an exemption had to do more than simply sign a form, called an administrative requirement.
Of the 36 bills, the researchers categorized five of them as restricting exemptions; three of those passed — in California, Vermont and Washington. They categorized 31 bills as expanding exemptions; none of those passed.
Of the 36 bills, 15 contained no administrative requirements, seven had one or two such requirements, and the remaining 14 had three to five administrative requirements.
Twenty states have personal belief exemptions, and in five of those states, a bill was introduced to restrict exemptions and in one a bill was introduced to expand exemptions.
Researchers writing in the journal Pediatrics who looked at the 2010 whooping cough outbreak in California suggested that clusters of nonmedical exemptions to immunizations were one of several factors. California had 9,120 cases of the illness, also called pertussis, or one-third of all the U.S. cases. Los Angeles had 1,000 of those cases.
Whooping cough is a respiratory ailment marked by bouts of coughing followed by a high-pitched noise when inhaling that can frighten parents -- hence the name. Before the introduction of vaccines, it was a leading cause of childhood death in the United States.
From 2000 to 2010, California's nonmedical exemption rates more than tripled, to 2.33%, with some schools reporting rates as high as 84%, the researchers said in Pediatrics. Both those clusters and the high pertussis clusters "were associated with factors characteristic of high socioeconomic status such as lower population density, lower average family size, lower percentage of racial or ethnic minorities," the researchers wrote.
The California Department of Public Health offers more information about the law at its Shots for Schools website.