I discuss my research on vaccination planning. Social interactions in treatment response make infectious disease a core concern of public health policy. Spread of infection creates a negative external effect. Preventive administration of vaccines may reduce disease transmission. In a decentralized healthcare system, infected and at-risk persons may not adequately recognize the social implications of their actions. Hence, there may be a rationale for government to seek to influence treatment of infectious diseases. Policies range from quarantines of infected persons to mandatory vaccination to subsidization of vaccines and drugs. I focus on a prevalent difficulty, being scarcity of evidence about how interventions affect illness. Randomized trials, which have been central to evaluation of treatments for noninfectious diseases, are less informative about treatment of infectious diseases. I develop minimax regret policy based on credible assumptions. I first consider a simple representative-agent setting in which members of a large population share identical cost of vaccination, cost of illness, probability of vaccine effectiveness, and probability of illness when unvaccinated or unsuccessfully vaccinated. I then generalize to vaccination of a heterogeneous population.