ABSTRACT
This chapter restricts attention to mass vaccination programmes and the changes they induce in the epidemiology of the infection, and in the population more widely. Such changes occurring at the population level are called impacts. Mass vaccination programmes with a safe and effective vaccine will produce enormous short- and long-term benefits for population health. However, as with any intervention applied on a large scale, they can also have more complex and sometimes counter-intuitive consequences, some of which may decrease population health or increase health inequalities. This chapter describes the different kinds of impacts of vaccination programmes and how they arise.
