California has tightened the laws that allow parents in the state to opt out of immunization for their children. It now joins Washington and Vermont in requiring parents who want an exemption to demonstrate that they have received factual information about the risks and benefits of vaccination from a health-care practitioner or the state’s health department. 

New Jersey is also considering a bill to strengthen exemption requirements, and similar legislation in Arizona has died in previous legislative sessions, but may be re-introduced next year. The issue is not a partisan one: bills have sponsors in both parties. And it has been recognized outside the medical community — although the California sponsor, Richard Pan (Democrat), is a paediatrician, most of the legislators have no medical background.

Each US state sets its own vaccination policies, and most will not generally allow children to attend public school unless they have been vaccinated against diphtheria, tetanus and pertussis (whooping cough); hepatitis B; the Haemophilus influenzae bacterium; measles, mumps and rubella; polio; and varicella (chicken pox). However, 20 states — including California, Washington and Vermont — allow exemptions for personal or philosophical belief, and 48 offer religious exemptions. All states permit exemptions for legitimate medical reasons.

But exemption rates are growing. In Washington, 6% of children entering kindergarten in 2010–11 had an exemption; in Vermont, the figure was 6.2%, compared with the US average of 1.5%. In California, exemptions rates rose by 25% between 2008 and 2010.