Figure 1.

Dynamics and duration of vaccine-induced immunity. The development of pathogen-specific immunity after vaccination can follow a number of different kinetic models. (A) Development of a measurable immune response can be determined, but if it does not reach above the protective threshold (indicated by the dashed line), then measurable immunity will note equate to protective immunity. Short-lived protective immunity (B) is common following primary immunization and is one of the reasons why most vaccines require booster vaccination. Long-lived protective immunity may be achieved by durable or nearly steady-state levels of immunity (C) or through the development of strong but rapidly declining immunity (D), if the starting point begins high in reference to the protective threshold. It is important to note that the protective threshold will differ by pathogen or disease and an immunological correlate of protection must be known in order to extrapolate the potential durability of a particular vaccine-mediated immune response.