ABSTRACT
This chapter turns to the issue of waning of vaccine effectiveness over time since vaccination. A separate chapter is dedicated to waning effectiveness since it commonly arises, is of public health importance and because assessing it is associated with specific methodological challenges. This chapter refers to age-specific vaccine effectiveness as the effectiveness of the vaccine when evaluated at a specified age, often some years after the vaccine was administered. This notion of age-specific vaccine effectiveness is particularly relevant for vaccines given in childhood according to a fixed schedule and is closely related to the issue of waning effectiveness over time since vaccination. It differs from the notion of vaccination-age-specific vaccine effectiveness (also often called age-specific effectiveness), which relates to the effectiveness of the vaccine when administered at a specified age.
