Figure 1.

Model-structure diagram of the epidemiology of gonorrhoea and vaccination

The population is divided into compartments representing different states of infection, with changes of state occurring through various processes. Individuals entering the sexually active population are uninfected, with those who receive adolescent vaccination (under the vaccination-before-entry strategy) entering the vaccine-protected stratum (1) and the remainder entering the unvaccinated stratum (2). When vaccine protection wanes, individuals are no longer protected and move from the relevant compartment in the vaccine-protected stratum to the corresponding compartment in the vaccine protection waned stratum (3). Individuals who become infected (4) pass through an incubating state, before either developing symptoms (5) and entering the symptomatic infection state, or remaining asymptomatic (6) and entering the asymptomatic infection state. Symptomatic individuals seek treatment (7) and enter the treatment state. Asymptomatic infections can be identified through screening followed by treatment (8), with individuals entering the treatment state, or there can be natural recovery (9), returning individuals to the uninfected state. All treated infections are cured (10, 11), with individuals who are vaccinated (under the vaccination-on-diagnosis or vaccination-on-attendance strategies) entering the vaccine-protected stratum (10) and those who are not vaccinated remaining in their current stratum (11)—infection does not confer natural immunity and recovered individuals are as susceptible as those never infected. Uninfected individuals who are vaccinated when screened (under the vaccination-on-attendance strategy) enter the uninfected state of the vaccine-protected stratum (12). Individuals leave the sexually active population through ageing from any state (13). Note that there are separate sets of compartments for groups of individuals with low sexual activity (darker grey layer) and high sexual activity (lighter grey layer), which have identical arrangements of compartments and vaccination-status strata; for clarity only flows in and out of the upper layer (the high sexual activity group) are shown.