Figure 1. . Schematic of the transmission model. The model is divided into nine age categories, with four subcategories per age group (not shown) based on different levels of sexual activity. In each period, uninfected persons can become infected. Infection rates are based on number of sexual partners per year, infectivity per infected partner, and percentage of potential partners who are infected. These variables are age- and risk-group specific. Infection rates for vaccinated persons also depend on the estimated vaccine efficacy. Percentage of potential partners infected includes partners within an age group and potential partners from younger and older age groups. Estimated mixing patterns between age groups differ by sex and age category.