05.06.2026 | Spreading phenomena
An epidemiologist observed the behavior of a new disease that emerged in southern Brazil 3 years ago. The data shows that 15% of a city's population always has the active virus at any time of the year. The figure below demonstrates the fraction of infected individuals over time. Which endemic model does the new disease follow? A. It is a disease following the SIR model, where, although part of the population builds resistance, in this model there is a transmission resistance to the outside of the city and it will always be present, even if the entire population is affected. B. It is a disease following the SIS model, in which individuals recover from the illness but do not develop permanent immunity, returning to the susceptible state. This continuous cycle allows the virus to circulate indefinitely, balancing the infection and recovery rates to maintain a stable endemic state of 15%. C. It follows the SI model, given that the virus remains active year-round. In this scenario, the...