No one likes injections, but most of us are glad to receive the many effective vaccines against infectious diseases such as measles and polio. In recent years, however, a growing anti-vaccine backlash has led to concerns over whether enough of our population is vaccinated against common diseases to prevent disease outbreaks taking hold.
In a new PLOS Medicine study, Peter Hotez, professor at Baylor College of Medicine and co-editor-in-chief of PLOS Neglected Tropical Diseases, and Melissa Nolan of the University of South Carolina worked with colleagues to analyze rates of nonmedical exemptions from childhood vaccinations throughout the U.S. I interviewed Hotez and Nolan via email about their findings and about the effect of such exemptions on the risk of infectious disease outbreaks.
What drew you to study epidemiology and global health?
MN: Through the years, I’ve come to learn that while we each have our own cultures, beliefs, and lifestyles, we all want to live a healthy life, belong to a community, and have the opportunity to thrive. Being a clinical epidemiologist allows me to help others pursue their goals by ensuring that they are healthy enough to do so. Epidemiology as a career is routed in scientific inquiry, and I enjoy the challenge of solving some of the most important clinical questions of our time through application of scientific rigor and innovative methodologies. Infectious diseases threaten us all, and stopping their transmission through novel public health approaches is a top priority for me.
Tell us about the U.S. childhood vaccination program. Why do some parents seek exemptions for their children?
PH, MN: As the CDC says, “vaccines are one of the greatest success stories in public health.” In the U.S., fifteen different vaccines are currently available for children, and recommendations are based on age group and medical indication. Estimates suggest that the U.S. childhood vaccination program has prevented 381 million infections and avoided 855,000 deaths. Despite these astounding public health successes, there is a growing movement opposing childhood vaccinations. Some children cannot be vaccinated for medical reasons, and these children rely on sufficient other children to be fully vaccinated to provide herd immunity. In contrast to this vulnerable clinical population, other reasons for nonvaccination include religious and philosophical beliefs. A major reason for philosophical belief-based exemptions is the erroneous belief that vaccines cause autism. Our current study aimed to better understand why some parents seek exemptions for their children.
In your study, you analyzed vaccination data from the 18 U.S. states that allow nonmedical exemptions from childhood vaccinations. What did you find out about trends in exemptions?
PH, MN: We found an increase in nonmedical exemptions in 12 of the 18 states that allow philosophical belief-based exemptions to childhood vaccinations. Additionally, we identified 15 clusters of high nonvaccinated populations (where more than 5 percent of all kindergarten-age children are unvaccinated) in these states. Statistical analysis verified that nonmedical exemptions do in fact correlate to a lack of measles, mumps and rubella (MMR) vaccination. Thus, our study identified several hot spots that have real potential for a measles outbreak.
Which areas have especially high exemption rates, and do they have any common features?
PH, MN: Fifteen metropolitan areas have elevated populations of nonvaccinated kindergarten-age children, mainly in states in the Western U.S., including Washington (Seattle and Spokane), Oregon (Portland), Arizona (Phoenix), Utah (Salt Lake City), Texas (Austin, Denton, and elsewhere), Missouri (Kansas City), and Michigan. We are currently executing a second study to evaluate what these populations have in common so we can better target public health education campaigns aimed at increasing vaccination uptake by these communities.
What most surprised or interested you about your findings?
PH, MN: In addition to these large cities having high counts of nonvaccinated children, we also found some lower-populated counties with high rates of nonmedical exemptions. Our analysis identified 10 counties with more than 14 percent of their kindergarten-age children unvaccinated, predominantly in the state of Idaho. Our findings would suggest that anti-vaccination sentiment is not restricted to large cities: there is also potential for vaccine-preventable disease outbreaks among more suburban or rural communities.
What are the implications of increases in nonmedical exemptions on the overall risk of infectious disease in children?
PH, MN: As larger unvaccinated populations grow, particularly in highly mobile cities, the potential for vaccine-preventable disease outbreaks grows. Measles outbreaks are of particular concern because measles is so highly transmissible and is associated with high morbidities, leading to hospitalization and sometimes permanent neurological injury or even death.
The measles virus is highly transmissible
What do you hope your findings might lead to, and what are the next steps for your research?
PH, MN: We hope this evidence-based study will help promote future research on this issue. Such studies could increase public policy support for physician and community education campaigns on the clinical benefits of vaccinating healthy children.
Research Article: Olive JK, Hotez PJ, Damania A, Nolan MS (2018) 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. https://doi.org/10.1371/journal.pmed.1002578
Images Credits: Olive et al., 2018; Anna Grove Photography; Brian Goldman; Dr. Erskine Palmer, USCDCP, Pixnio CC0