Incidence of Vaccine-Preventable Diseases Shapes Legislation

In the 2018-19 school year, the number of children whose parents took advantage of vaccine exemptions increased for a third consecutive year. As the frequency of vaccine-preventable diseases increases in the United States, susceptible, nonimmune children with exemptions have fueled disease transmission. Previous research has shown that despite this climate, state legislators nationwide have continued to introduce legislation which expands exemption opportunities.

A new research letter published in JAMA Pediatrics sought to investigate the association between vaccine-preventable disease incidence and state vaccine exemption legislation. The study found that incidences of vaccine-preventable disease were associated with an increase in legislation which would restrict vaccine exemptions.

Results were collected by linking a preexisting data set of proposed vaccination-related bills to data on vaccine preventable disease that was submitted to the National Notifiable Diseases Surveillance System. Study authors focused on the 2010 to 2016 period and left a 1-year gap to allow time for upticks in disease to trigger a legislative response.

National Notifiable Diseases Surveillance System data was filtered to focus on tetanus, diphtheria, Haemophilus influenzae serotype B, hepatitis A and B, influenza, pneumococcal disease, measles, meningococcal disease serotypes A, B, C, Y, and W-135, pertussis, rubella and congenital rubella syndrome, mumps, and varicella. This selection of diseases was determined by the Advisory Committee on Immunization Practices childhood schedule.

Vaccine-preventable diseases were correlated with subsequent legislative activity. Legislative activity was operationalized as counts of bills which restricted or expanded the ability to exempt children from school-entry vaccine requirements. Investigators used Poisson mixed-effects regression models to account for correlations within states and control for secular trends.

A sensitivity analysis altered the independent variable from vaccine preventable diseases generally to pertussis. Pertussis was selected for sensitivity analysis because several outbreaks had garnered widespread attention, which investigators hypothesized could be related to legislative action during the study period.

Each state studied reported a mean of 25 vaccine preventable diseases per 100,000 people annually. A total of 175 vaccine exemption-related bills were included, 92 of which expanded exemptions and 83 of which restricted exemptions. When analysis was limited to bills which restricted exemptions, each standard deviation increase in vaccine-preventable diseases per 100,000 was associated with 54% more bills being proposed (95% confidence interval, 27%-88%).

In the analysis of bills expanding exemptions, reported vaccine-preventable diseases were not statistically associated with bill proposals. However, when vaccine-preventable disease was restricted to pertussis the sensitivity analysis revealed significant associations with both expansive and restrictive types of legislation.

Investigators expressed optimism about the results, in light of increasing vaccine hesitancy and misinformation. Their results suggest that social responses to outbreaks may shift political attitudes around vaccine exemption.

Study authors explained that they believed upticks in vaccine preventable disease prompted media coverage, raised public awareness, and triggered a political response to these social-level changes. They wrote that “counter to the conventional examination of how laws affect health, we flipped the model to explore how health is associated with legislative activity.”