Ending nonmedical vaccine exemptions increased vaccination coverage at the state and county levels in California and boosted herd immunity, a new study finds.
Published in December in Plos Medicine, the study examined a 2016 California law that eliminated nonmedical vaccine exemptions, finding that the strategy increased measles-mumps-rubella vaccinations among state schoolchildren. Before the law, parents and caregivers were allowed to cite personal beliefs as a reason to exempt their children from vaccines required for attendance at state schools.
Recent measles outbreaks in the U.S. have fueled a push to end such exemptions. More than 1,280 measles cases were confirmed in the U.S. in 2019, the most since 1982, according to the Centers for Disease Control and Prevention. That same year, Mississippi, New York, Washington and West Virginia passed laws to end nonmedical exemptions in their states.
School immunization requirements have been successful in the U.S. at reducing vaccine-preventable diseases. But 45 states still allow children to be exempt from vaccinations for nonmedical reasons, according to a 2019 report from the Pew Research Center.
For the new study, researchers looked at data on vaccinations and coverage exemptions in children entering kindergarten. The dataset included information on 45 states between 2011 and 2017 and county-level data from 17 states between 2010 and 2017. Researchers estimated how many California children would have received an MMR vaccination without the law, and how many children were likely vaccinated under the new law.
They found the 2016 law was associated with a 3.3% increase in vaccination coverage at the state level and 4.3% increase at the county level. The largest increases were in high-risk counties, meaning counties that had the most children not vaccinated prior to law implementation. Overall, vaccine coverage increased 10% to 20% in the high-risk counties, according to Nathan Lo, MD, PhD, a medical resident at the University of San Francisco and senior author of the study.
The 2016 law also also boosted herd immunity in California, the study found. When 95% of people are vaccinated in a region, herd immunity is achieved for measles and other diseases. Herd immunity helps prevent diseases from spreading to vulnerable populations, such as newborns, seniors, people with compromised immune systems and those who cannot receive vaccinations for medical reasons.
In 2015, prior to the California law taking effect, vaccination rates in the state were below herd immunity at 92.8%, the study said. In 2017, after the law had taken effect, herd immunity was achieved, with rates rising over 95%.
“Even small average increases can have a big effect,” Hannah Karpel, a student at New York University School of Medicine, and co-author of the study, said in a news release.
For more information, visit https://journals.plos.org/plosone.
- Copyright The Nation’s Health, American Public Health Association
