Abstract
After an initial infection, the risk of reinfection by the same infectious agent is often altered. The immunity conferred may be complete or partial, permanent or temporary; it may protect against reinfection or only against the onset of symptoms. In some cases, it may be suboptimal due to complex phenomena such as original antigenic sin, in which the immune system tends to preferentially reactivate the memory response directed against the first strain encountered, rather than against the current variant. In this course, I will show how the spread dynamics and severity profile of an infectious agent are largely shaped by the nature of the immunity conferred by infection and vaccination. I will describe how mathematical models are used to assess the impact of vaccines and optimize vaccination strategies.
