Model structure diagram of gonorrhea transmission in different sexual activity groups.

The model categorizes individuals into uninfected, incubating, infected (asymptomatic or symptomatic), and treated compartments. The model characterizes a constant population over time by incorporating individuals who enter (1, 2) and leave (13) sexually active age. A certain proportion of the population is initially set to be infected, while the remainder were deemed uninfected. Uninfected individuals (green compartments) who have had sexual contact with infected individuals may be exposed to and get infected with gonorrhea (4). Those in the incubating stage will develop either symptomatic (5) or asymptomatic (6) infection, and they can spread gonorrhea to the uninfected population through sexual contact (orange compartments). Individuals with either symptomatic or asymptomatic infection are assumed to seek treatment or regular sexually transmitted infection (STI) screening from sexual health clinics (7, 8) with some probability. However, individuals with asymptomatic infections can recover naturally (9). Both asymptomatic and symptomatic infections are diagnosed through laboratory tests, and can be cured from treatment and remain non-infected shortly (blue compartments) before returning to the susceptible compartment (11). Vaccination is offered in school-based programme aimed at male teenagers entering sexually active age (1), or upon diagnosis (11) and/or screening (12) in sexual health clinics, based on different vaccine administering programme (blue arrows). Identical arrangements of gonorrhea transmission-vaccination processes are specified for both high and low sexual activity groups (light and dark gray panel), while accounting for heterogeneity in epidemiological parameters in both groups.