The repeal of nonmedical vaccine exemptions in California was only partially effective in improving vaccination coverage, according to a working paper issued by the National Bureau of Economic Research.

Chelsea J. Richwine and colleagues from George Washington University in Washington, D.C., used county-level vaccination and exemption rates at kindergarten entry to estimate the impact of California's repeal of nonmedical exemptions on immunization coverage for school-mandated vaccines.

The authors found that compared with control states, vaccination coverage increased for all required vaccines following the California repeal. Coverage rate increases ranged from 2.5 percent for measles-mumps-rubella vaccination to 5 percent for polio vaccination. There was also a significant 3.4 percentage-point decline in nonmedical exemptions, accompanied by a 2.1 percentage-point increase in medical exemptions in counties that previously had high rates of nonmedical waivers.

"Our findings indicate that the repeal of nonmedical exemptions in California was only partially effective in improving vaccination coverage, and may have led parents to substitute between medical and nonmedical exemptions, leading to a net decline in total exemptions of just 1 percentage-point," the authors write.

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