Relaxed state vaccination laws may be contributing to lower immunization rates and higher outbreaks of preventable diseases like pertussis and measles, a new study has shown. Findings from the study are published in Health Affairs.

Researchers from the University of Georgia found higher rates of pertussis in states that allowed philosophical exemptions and used a standardized exemption form. Religious and philosophical reasons are categorized as nonmedical exemptions. Currently all but three states allow exemptions for religious reasons, only 17 allow philosophical exemptions, and 39 use a standardized exemption form.

Study authors used exemption data collected by the Centers for Disease Control and Prevention (CDC) for kindergartners in the 2002–12 annual school assessment reports. They found three key policies that lower rates of pertussis:

  • Requiring state health department approval for nonmedical vaccination exemptions
  • Allowing exemption from only specific vaccines instead of all vaccines
  • Levying criminal and civil punishment against those who do not comply with vaccination policies

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Mississippi, West Virginia, and California were found to have the strictest vaccination laws in the country. The nine states with the least effective laws are: Colorado, Idaho, Michigan, Minnesota, Texas, Utah, Vermont, Washington, and Wisconsin. The 18 states with the most effective exemption policies are: Alabama, Arkansas, Delaware, Florida, Indiana, Iowa, Kansas, Kentucky, Maryland, Massachusetts, Missouri, Montana, Nebraska, Nevada, New Mexico, North Carolina, South Dakota and Tennessee.

The decrease in the number of vaccinated individuals contribute to a loss of “herd immunity” and thus diseases once mostly eliminated from the United States are rising.

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