Long-term survivors in an epidemic without recovery

The analysis of epidemics without recovery often implies the inclusion of long-term survivors in the modeling process. Such individuals are characterized by a peculiarly long sojourn in a state of infection without any sign of progression towards the subsequent evolutionary state of the disease. A parametric modeling of their presence in an epidemic involves non-Markov staging of the infection process and of its development. In the present work, an approach involving survivor function is proposed, along with some remarks on epidemiological indicators and some numerical and graphical examples of its application.