New disease model pits zombies against clerics for clarity

    Epidemic modeling requires nuanced approach for diseases such as HIV

    February 9, 2023


    The world of disease modeling studies the dynamics of how susceptible individuals become infected and eventually recover, which gives rise to the classical Susceptible-Infected-Recovered model and its variations. In these models, an infected individual who does not ever recover is sometimes called a “zombie.”

    A new variation of the Susceptible-Zombie-Removed (SZR) model adds in another player: the cleric, who can cure the zombies, thus accounting for direct medical intervention that can reduce disease spread even if the outbreak cannot be completely cured.

    “In the original SZR models, there are only interactions between susceptibles and zombies,” said principal investigator Cynthia Reichhardt of Los Alamos National Laboratory. “Such interactions result in either the susceptible becoming infected, or the zombies reaching the recovered, sometimes also called the removed or noninfectious state.”

    “In our model, susceptibles cannot change the state of a zombie, but still might become infected and turn into zombies themselves,” she said. “Only clerics have the power to cure a zombie, changing their state from infected to recovered — and the clerics can also be turned into zombies. Zombies more easily infect susceptibles than clerics, which is how we capture the idea that medical personnel take better precautions against infection, such as proper wearing of surgical masks, than members of the general populace.”

    The addition of clerics to the model is aimed at providing more accurate modeling of infectious chronic diseases that are controlled through medical interventions. The new variation of the model is known as Susceptible-Cleric-Zombie-Recovered (SCZR).

    While casting the model in movie-type terms stimulates discussions, this new model is of practical value to model certain real-world diseases such as HIV and HCV (Hepatitis C Virus) that, if left untreated, confer a lifelong ability to infect, yet when suitably treated can allow infected individuals to recover fully or functionally.

    Reichhardt points out that “the SCZR model is a good starting point for creating new types of epidemic models in which treatment is needed for recovery and there are finite or limited treatment resources available.”

    Paper: “Transition from Susceptible-Infected to Susceptible-Infected-Recovered Dynamics in a Susceptible-Cleric-Zombie-Recovered Active Matter Model,” Physical Review E, DOI: 10.1103/PhysRevE.107.024604

    Funding: Work at Los Alamos was sponsored by Los Alamos National Laboratory and the Los Alamos Center for Nonlinear Studies.