State legislatures across the US are trying to increase the number of children who receive vaccinations against disease by enacting laws that make opting out of those shots tougher for parents. California, Vermont, and Washington—states that allow parents to decline scheduled vaccinations for their children for personal or philosophical reasons—require parents opting out to provide proof that a health-care practitioner or representative of the state's health department gave them scientific information about the risks and benefits of those vaccinations. State lawmakers in New Jersey and Arizona have floated ideas for similar legislation.
Even in the face of recent outbreaks of whooping cough and other diseases, vaccine exemption rates are rising across the nation. An average of 1.5 percent of US children entering kindergarten in 2010-2011 had an exemption, and rates in some states are even higher. "There really is a problem when you don't have herd immunity so that you can stop the infectious diseases," Washington Senator Karen Keiser (D) told Nature. The problem risks becoming worse in states, such as Kansas, Mississippi, Massachusetts, South Dakota, and West Virginia, that have recently tried to enact laws that permit philosophical exemptions. But states that have strengthened exemption requirements are already seeing positive results. Washington, for example, has seen kindergarten exemption rates drop to 4.5 percent this year from 6 percent last year.