Each of these interventions incurs a quantifiable cost: culling results in additional deaths; medical treatments or quarantines result in monetary expenses; vaccination incurs both monetary expenses, and in some cases additional vaccine-induced infections. Additionally, in many situations the costs associated with each of these actions can depend upon the state of the disease within the population of interest. For example, per-dosage prices of vaccine can increase as resources become scarce as a result of an aggressive vaccination campaign. Similarly, vaccine efficacy can decrease as a result of selection for drug resistance. Such observations raise the question of how to find optimal interventions that adaptively depend on the state of the epidemic.