In 2014, a national measles outbreak was linked to Disneyland, where at least 39 cases were traced to direct exposure to the disease at the park. Over 170 people in 21 states became infected. In California,
88 percent of the measles patients were either unvaccinated or had unknown or undocumented vaccination status.
This caused the largest US measles outbreak in decades, with 667 confirmed cases.
People have a variety of reasons for not vaccinating their children, but all philosophical and religious reasons fall into a category of vaccine exemptions called “Personal Belief Exemptions.” These exemptions are separate from medical exemptions.
A study of California kindergarteners
sought to figure out who are using non-medical exemptions to prevent vaccinations.
The study obtained publicly available Personal Belief Exemption (PBE) data for kindergarteners in the 2007-2008 and 2013-2014 school years for 6911 California schools from the California Department of Public Health’s “Immunization levels in child care and schools” pages. Income, education, and race of the parents as well as school
characteristics were examined.
The following graph traces the percentage increase in PBEs according to a $25,000 increase in median household income up to $150,000. The data revealed that with each $25,000 interval, there was a nearly linear percentage increase in PBEs.
The research paper stated that PBEs were nearly twice as common in private schools (5.43 percent) as public schools (2.88 percent) in 2013. The table below displays the 2016-2017 Kindergarten Immunization Assessment from the California Department of Public Health’s Immunization branch.
Both the 2015-16 data and 2016-17 data show that immunization exemptions of all kinds are higher in private schools than public schools, and private schools have lower immunization rates. There is a notable jump in permanent medical exemptions along with an increase in overall vaccination rates between the two years. This is due to California Senate Bill 277,
which passed in the summer of 2015 to remove personal belief expeditions in response to the Disneyland measles outbreak.
While neither of these studies found strong relationships between the education level of the parents and vaccination rates, the 2013 data found higher education attainment was associated with small increases in PBEs. The rate of change of PBE percentages from 2007 to 2013 was also slower for more educated areas. For example, a 10 percent increase in the percentage of the population with a college degree was associated with a 0.025 percent decrease in the annual rate of growth in PBE percentages. More college degrees meant a slower rate of change.
The Centers of Disease Control and Prevention releases yearly reports on United States child vaccination rates, viewable in their ChildVaxView page.
The scatterplot below was created using data from the 2017 Childhood Sociodemographic Characteristics Report
and the 2017 Childhood Measles, Mumps, and Rubella (MMR) Vaccination Coverage Report.
Scatterplot Info: PercentVax stands for the percent of children who received at least one dose of the MMR vaccine by 35 months old and PercentWhite is the percentage of the population that identifies as non-Hispanic white. The size of the dots, PercentPoverty, represents the percent of the population living under the poverty line based on family income and household size using the US Census poverty thresholds for the year immediately prior to the survey. PercentUrban is the percent of the population living in urban areas based on the number of people living in a metropolitan statistical area central city. The y-axis of the plot begins at 80% vaccinated to make the data easier to view. California is represented by a large, teal-colored dot on the far left of the graph under a cluster of purple dots.
The scatterplot suggests that, on a national level, there is not a strong association between locations with a mostly white population and highly vaccinated populations. States with lower poverty rates do not consistently vaccinate their children more than states with high poverty rates, and children living in urban areas are no more likely to be vaccinated than other children. The scatterplot shows that compared to other states, California has a lower population of non-Hispanic white people and is clustered with other more urban locations with medium-high poverty rates. Further state-by-state research would need to be conducted to determine if California is the only location with a trend of unvaccinated children in white, wealthy areas. At this time, it seems that Califorina is an anomaly.