THE RISKS OF VACCINE HESITANCY AND REFUSAL: A CASE STUDY OF MEASLES OUTBREAKS IN SWANSEA, WALES, AND KNOX COUNTY, OHIO

Abstract

Vaccine hesitancy and refusal, a growing trend in recent years, hinders the elimination and eradication of diseases. This thesis looks investigates the extent to which the anti-vaccine movement impacts vaccine coverage and creates opportunities for epidemics to occur. Measles virus has been controlled globally and especially in the developed world through vaccination programs with the MMR vaccine, which when administered as a two-dose regimen has 95-100 percent efficacy. However, in recent years, the U.S. and U.K. have seen increases in incidence of the disease. A case study of two recent measles outbreaks, a 2012-2013 outbreak of 1,202 notified cases in Swansea, Wales and a 2014 outbreak of 383 cases among the Amish in Ohio, serves as the basis for investigating the role of vaccine refusal on outbreak. In both outbreaks, low vaccine coverage rates associated with vaccine hesitancy and refusal compromised herd immunity and allowed for the spread of disease among communities where measles is no longer endemic. The reintroduction of eliminated viruses into these undervaccinated populations represents a new challenge to public health control teams. Therefore, this thesis looks at reactive responses to this sort of outbreak with low routine vaccination coverage. The potential efficacy of vaccination and behavioural interventions is investigated using a parameter sweep of a theoretical SIR model. The model shows that both interventions can be used to reduce incidence given a sufficiently significant intervention with time constraints post onset of outbreak. The case study shows the consequences of vaccine refusal in communities, and provides insight into a changing risk-benefit analysis in deciding whether or not to vaccinate.