The classical formulation of the catalytic model assumes that the force of infection, whether age dependent or not, is constant over time Griffiths 1974.  Whitaker and Farrington Whitaker 2004 illustrated that the estimates of the classic method were robust to the annual and multi-annual cyclic fluctuations commonly seen for many childhood infections. However, in the era of vaccination control, we have observed large directional changes in prevalence of many infections; e.g. a 78% reduction in measles cases between 2000-2012 Simons 2012, the elimination of rubella from the Americas [REF-PAHO statement ]. The basic principles of the catalytic model suggest that, even in the absence of reporting of total cases, these declines in disease prevalence should be reflected in the changing age distribution of infection or sero-prevalence. Though long-term age-specific surveillance is rare for most infections, Ferrari et al Ferrari 2013 performed a comparative analysis of the age distribution of measles cases between 2001-10 to quantify the impact of increased vaccination on measles force of infection. Over that time period there was a strong correlation between first dose measles vaccination coverage and the mean age of infection.  The slope of this relationship was mediated by the birth rate, with vaccination having smaller impact on the mean age of infection in high birth rate settings. This comparative analysis suggests the pattern that is expected to be observed as countries continue to increase vaccination coverage over time.