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Measles Vaccine Hesitancy and Spatial Clustering of Vaccine Exemptions: A Setup for Future Outbreaks

December 14, 2021

All of us are focused on vaccinated children 5 years and older for COVID-19 in hopes of reaching herd immunity and hopefully preventing future outbreaks of new strains. Sadly, outbreaks among unvaccinated individuals will likely still be common. Certainly, this has been true for other infectious diseases, such as measles, and will likely be a recurrent problem given under-vaccination. We can learn a lot from these experiences, including predicting future hotspots. Consider a study we are early releasing this week by Gromis et al (10.1542/peds.2021-050971).

The authors of this study used modeling to demonstrate how spatial clustering of non-medical exemptions in youth ages 0-17 years might contribute to outbreaks of measles before and after California Senate Bill 277 (SB277) was passed in 2015. This bill eliminated non-medical personal belief vaccine exemptions, which had been increasing prior to the bill’s passing and appeared to be clustered within and across schools in California. Gromis et al modeled what would happen if medical exemptions increased or stayed unchanged after SB277, what if there were no clustering, and what if immunization levels decreased despite SB277. Even with a high overall rate of vaccination in their various models, the authors demonstrated that spatial clustering of medical exemptions would still threaten local herd immunity, and if you add in low overall immunization rates to measles above and beyond medical exemptions, a major outbreak or even an epidemic of measles could ensue. 

As you might imagine, the take-aways from this modeling study by Gromis et al do not stop with measles outbreaks. To show the concern special clustering and vaccine hesitancy can have on prolonging or worsening the current pandemic, we invited three infectious disease experts to weigh in with an accompanying commentary to this study—Drs. Yvonne Maldonado and Sean O’Leary (chair and co-chair of the AAP’s Committee on Infectious Diseases) and Dr. Peter Hotez (Professor of Pediatrics and Molecular Virology and Microbiology from Texas Children’s Hospital) (10.1542/peds.2021-054369). This study and commentary demonstrate how concerning the combination of vaccine hesitancy and clusters of exemptions have been for measles but also for the current pandemic and offer suggestions for what we can do as pediatricians to work with our patients, communities, and our state public health systems to ensure that preventable infectious diseases do not experience a major resurgence, which none of us want to see happen.

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