Despite advances during the twentieth century, immunization coverage is far from universal and faces significant obstacles in both developing and developed countries. Weak policy emphasis on vaccination may be the result of the narrow view of its benefits in scientific and policy-making communities, which focus mainly on the averted costs of medical treatment. An investigation of the broader impacts of immunization shows that the benefits of vaccine programs—in particular, their economic effects via improved health—have been underestimated, thereby causing the rate of return to be underestimated.