Figure 2.

Estimating Historical Patterns of Infection from Age-stratified Serological Surveys. The panels show how the history of circulation of a pathogen (A) is expected to impact age-stratified seroprevalence when immunity is life-long (B) or temporary (C). In the red scenario, an epidemic infecting 30% of the population occurred 15 years ago. If immunity is life-long, the seroprevalence is expected to be 30% among those aged ≥15 years but null among younger individuals (B). In the blue scenario, low-level continuous circulation of the pathogen (A) is expected to lead to a slow increase of seroprevalence with age (B). In the case of waning immunity, a plateau in seroprevalence for older individuals may be expected (C). Catalytic models were developed to reconstruct the history of circulation of the pathogen from serological surveys. The force of infection is the annual probability a susceptible individual will become infected.