Evaluation of community-level effects of intervention programs in infectious diseases is receiving increased attention. In this paper, we consider evaluation of the community-level effectiveness measures on the example of vaccination of children against influenza. We introduce the concept of the epidemic prevention potential (EPP) as a measure of the ability of an intervention to either prevent transmission or at least to keep it below a pre-defined limit. As a concept to describe the general ability of an intervention to limit outbreaks to a certain defined size, the term EPP fills a void. We constructed a stochastic simulation model of influenza transmission and vaccination in a structured community to illustrate the effectiveness measures of interest and the epidemic prevention potential. The concepts are general and could be applied to other interventions, such as antivirals and quarantine.