Eradication campaigns become more difficult the closer they are to success Prevalence determined by herd immunity of population responsiveness of vaccine demand to prevalence rates As disease prevalence decreases,demand for self protection decreases Prevalence allowing disease to rebound Vaccination rate In some cases,the only way to ensure the last few vaccinate is a subsidy or government mandate Bhattacharya,Hyde and Tu-HealthEconomicsBhattacharya, Hyde and Tu – Health Economics Eradication campaigns become more difficult the closer they are to success  Prevalence determined by  herd immunity  responsiveness of vaccine demand to prevalence rates  As disease prevalence decreases, demand for self protection decreases allowing disease to rebound  In some cases, the only way to ensure the last few vaccinate is a subsidy or government mandate