California passed legislation last week removing the "personal belief" exemption from the state's vaccine requirements for children. The impetus to the measure was the outbreak of measles in Disneyland in January, which spread mostly through unvaccinated children. The outbreak revealed that antivaccination concerns had grown so widespread that more than one-half the children in some schools were unvaccinated. California state Sen. Richard Pan, who is also a pediatrician, introduced SB 277 to remove personal and religious exemptions from vaccines in the state. Every state in the United States requires children to be vaccinated in order to attend public schools. Under California's current law, parents can opt out of vaccines for their children for almost any reason, simply by claiming a "personal belief" exemption. Observers note that vaccines have been so successful that most people do not even remember the era when these diseases were a constant fear of childhood, making it easier for vaccine opponents to spread erroneous claims that such immunization efforts cause harm.