1. This study predicted an increase in the incidence of measles cases and outbreak size using a stochastic mathematical model calibrated using published cases in the United States. The increased number of cases was associated with significantly increased medical cost.
2. Elimination of non-medical exemptions to increase MMR vaccine adherence predicted there would be a reduction in the annual incidence of measles cases in the United States by 20%.
Evidence Rating Level: 3 (Average)
Study Rundown: In recent years, misinformation regarding vaccine safety has led to declining rates of childhood vaccination in the United States through parental non-medical exemptions based on personal beliefs. Reduction in vaccination adherence is a major public health concern due to the increased risk of outbreaks of childhood illnesses. The current study sought to accurately model measles outbreaks as a function of vaccination rate using data available from the US Center for Disease Control and Prevention (CDC). Economic cost associated with increased case rates were estimated using published literature. The study found nationwide MMR vaccination rate was 93%. A 5% reduction in vaccination rate was associated with a threefold increase in the number of annual measles cases with an estimated cost of $2.1 million annually. Elimination of non-medical exemptions to vaccinations was estimated to increase MMR vaccination rates to 95% and lower measles incidence by 20%.
The main strengths of the model included the validation using data from England and Wales, and sensitivity analysis describing variation in results but an overall conservative estimate of potential costs associated with declining MMR vaccination rates. The main limitations of the results were in the reliance of population wide data with state-level variation in reporting standards for vaccine rates and disease cases, and assumptions made in the basic reproductive number associated with measles.
In-Depth [mathematical model]: This study obtained data from the US CDC and state-level reports of MMR vaccination rates from 2010-2015 and national data from 2007-2008 from representative counties to estimate vaccine rate variation. Measles outbreaks were modeled based on two chance events: imported measles cases from travelers and exposure to susceptible children, and subsequent outbreak size. The model was calibrated using data from the United States and validated using data from England and Wales. Cost per case of measles was obtained from prior literature and estimated to be $20 000.
MMR vaccination rates were estimated at 93% (87-97% state variation) with rates of non-medical exemption of 2% (0.4-6.2% state variation). In the developed model there were 48 annual cases of measles with a 5% reduction in vaccination rate estimated to increase this incidence to 150 per year. This is associated with an annual cost of $2.1 million. Eliminating non-medical exemptions was estimated to increase MMR vaccination prevalence to 95% and reduce annual incidence to 38 cases.
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