Preferred policies, having the highest probability of having the greatest net benefits, at 30% vaccine efficacy. a) Preferred policies at a willingness-to-pay of US $36,000, as vaccination cost increases. b) Preferred policies with vaccination costs sampled uniformly from the range ($10, $300), as willingness-to-pay increases. Vertical dashed lines indicate the very cost-effective threshold (US $12,000) and the cost-effective threshold (US $36,000).