The U.S. is currently facing a nationwide measles crisis. The rising rate of non-medical exemptions is a driving force behind these outbreaks, as parents cite religious or philosophical reasons for the decision not to vaccinate their children. In a new working paper published in the National Bureau of Economic Research, Chelsea J. Richwine, Avi Dor, and Ali Moghtaderi of George Washington University examine the effect of California’s 2016 decision to repeal all non-medical exemptions on immunization coverage.


After California’s 2015 measles outbreak in Orange County, which ultimately infected 110 Californians and at least 15 others in neighboring states, the state moved to repeal all non-medical exemptions. To find out whether the repeal was associated with an increase in uptake of vaccines required for school entry, the research team tracked vaccination rates from 2012 to 2017 in California and a group of control states that did not have any changes in their exemption provisions.

Their analysis indicates that:

  • California’s policy change significantly improved vaccination coverage by an estimated 2.5 to 5 percent.
  • There was a 3.4 percentage-point decline in non-medical exemptions, but a 2.1 percentage-point increase in medical exemptions in counties that previously had high rates of non-medical waivers.

Implications for Policy and Practice

Despite measles being declared officially eliminated from the U.S. in 2000, misplaced fears about vaccine safety have led more and more parents to seek out exemptions for their children. We are now at a breaking point in our national immunization policy strategy. But as lawmakers consider tightening exemption standards, including eliminating all non-medical exemptions, they would be wise to note potential unintended consequences of policy action.

Following the California law change, the increase in medical exemptions accounted for nearly two-thirds of the decline in non-medical exemptions. That it was apparently easy for parents to successfully receive medical exemptions speaks to a dangerous flaw in our health care system. Policymakers and public health professionals may need to consider strategies to enhance monitoring of physician allowances of medical exemption waivers. Until we do, pockets of unvaccinated children in New York State, California, Washington, and other states present a very real threat to the health and well-being of our youngest and most vulnerable citizens.