Modeling Measles Transmission in the North American Amish and Options for Outbreak Response.

Measles outbreaks in the United States continue to occur in subpopulations with sufficient numbers of undervaccinated individuals, with a 2014 outbreak in Amish communities in Ohio pushing the annual cases to the highest national number reported in the last 20 years. We adapted an individual-based model developed to explore potential poliovirus transmission in the North American Amish to characterize a 1988 measles outbreak in the Pennsylvania Amish and the 2014 outbreak in the Ohio Amish. We explored the impact of the 2014 outbreak response compared to no or partial response. Measles can spread very rapidly in an underimmunized subpopulation like the North American Amish, with the potential for national spread within a year or so in the absence of outbreak response. Vaccination efforts significantly reduced the transmission of measles and the expected number of cases. Until global eradication, measles importations will continue to pose a threat to clusters of underimmunized individuals in the United States. Aggressive outbreak response efforts in Ohio probably prevented widespread transmission of measles within the entire North American Amish.

Individual-based modeling of potential poliovirus transmission in connected religious communities in North America with low uptake of vaccination.

BACKGROUND: Pockets of undervaccinated individuals continue to raise concerns about their potential to sustain epidemic transmission of vaccine-preventable diseases. Prior importations of live polioviruses (LPVs) into Amish communities in North America led to their recognition as a potential and identifiable linked network of undervaccinated individuals. METHODS: We developed an individual-based model to explore the potential transmission of a LPV throughout the North American Amish population. RESULTS: Our model demonstrates the expected limited impact associated with the historical importations, which occurred in isolated communities during the low season for poliovirus transmission. We show that some conditions could potentially lead to wider circulation of LPVs and cases of paralytic polio in Amish communities if an importation occurred during or after 2013. The impact will depend on the uncertain historical immunity to poliovirus infection among members of the community. CONCLUSIONS: Heterogeneity in immunization coverage represents a risk factor for potential outbreaks of polio if introduction of a LPV occurs, although overall high population immunity in North America suggests that transmission would remain relatively limited. Efforts to prevent spread between Amish church districts with any feasible measures may offer the best opportunity to contain an outbreak and limit its size.