A new study of school vaccination requirement exemption rates shows that clusters of children with exemptions are present in many local areas and that actual measles, mumps, and rubella (MMR) immunization rates are lower in those clusters. The researchers looked at the geography of exemptions in states that allow personal belief or philosophical belief exemptions (PBEs). States with a large number of highly exempting communities include Utah, Idaho, and Texas. Highly exempting areas are not necessarily located in large urban areas; in fact, “the 10 counties with the highest NME [non-medical exemptions] rates in the country have fewer than 50,000 persons and are located in rural regions.” However, many large urban areas have a high number of exempted kindergartners, defined in the study as 400 kindergartners. These include Phoenix, Salt Lake City, Provo, Seattle, Spokane, Portland, Troy MI, Warren MI, Detroit, Houston, Fort Worth, Plano, Austin, Pittsburgh PA, and Kansas City, MO. This latter information is concerning because the areas could have a large enough number of unvaccinated children to affect herd immunity protection, particularly with regard to the spread of measles, which is highly communicable.
In 12 of the 18 states, rates of NMEs have been increasing since 2009. Some states seem to have had a leveling off of exemption rates, but in Arkansas, North Dakota, Ohio, Oklahoma, Texas, and Utah, NME rates continue to increase.
In many of the 18 states studied, the PBE exemptions may also allow for religious belief exemptions, but the study did not assess states that allow solely religious belief and medical exemptions (for example, New York and New Jersey don’t allow PBEs but do allow religious exemptions and they are not included in the study). In many cases, officials in states with only religious belief exemptions have a broad view of religious belief that extends to parental beliefs others would most likely classify as PBE. It may be that in these areas patterns of exemption and non-vaccination are similar to those of areas with PBE exemptions.
It seems obvious that communities with high rates of immunization exemptions, and thus low immunization rates, pose a risk to inhabitants of those communities. But what are the broader risks of these hot spots? Paul Delamater at University of North Carolina has studied the spatiotemporal characteristics of changing NME rates in California. (Until just a few years ago, California allowed for personal belief exemptions for school vaccination requirements; however, legislation passed in 2015 after the Disneyland measles outbreak eliminated all but medical exemptions.) Delamater looked at NME use from 2000-2013, and found a common pattern: use of NMEs spreads out from areas of high NME use. It’s almost as if NMEs spread like an infectious disease from a patient zero — in this case, a local area with high NME use — to others. The pattern held for densely populated as well as rural areas in the state. His findings show that hot spots of refusal don’t exist in a vacuum: they have the potential to spread widely. Delamater did not study the mechanism of spread, and future study may find that it is related to linked social networks, local area provider practices, or any number of other factors.
Delamater, in a different study, also looked at the use of medical exemptions in California schoolchildren after the 2015 legislation eliminating NMEs went into effect. Medical exemption rates increased from 0.17% of kindergartners in 2015 to 0.51% of kindergartners in 2016. The total exemption rate fell from 2.54% to 1.06% of California kindergartners.
The use of PBEs may need to be treated with targeted surveillance and tracking in areas with high NME use to prevent their spread, with educational campaigns specifically designed to reach vaccine-hesistant parents, and with outreach to local health-care providers on how to communicate with hesitant parents. Legislative efforts to reduce availability of PBEs may also help to contain the diffusion of PBE use into vulnerable communities.
Delamater PL, Leslie TF, Yang YT. Examining the spatiotemporal evolution of vaccine refusal: nonmedical exemptions from vaccination in California, 2000–2013. BMC Public Health. 2018 Dec;18(1):458.
Delamater PL, Leslie TF, Yang YT. Change in medical exemptions from immunization in California after elimination of personal belief exemptions. JAMA. 2017 Sep 5;318(9):863-4.
Live JK, Hotez PJ, Damania A, Nolan MS. The state of the antivaccine movement in the United States: A focused examination of nonmedical exemptions in states and counties. PLoS Med 15(6): e1002578.