The SIS mannequin is a really primary mannequin in epidemiology. It represents Inclined (S), Contaminated (I), and Inclined (S) teams of individuals. It’s used to know ailments with a better fee of reinfections. Within the SIS mannequin, there are solely two compartments – persons are both inclined to an infection or contaminated. The mannequin assumes that there’s direct transmission between people who’re contaminated and inclined. Within the SIS mannequin, there isn’t any ‘Recovered’ group of individuals – as soon as persons are not contaminated, they transfer to the inclined class, the place they might be contaminated once more.
Advantages of the SIS mannequin
The SIS mannequin is used when ailments have a excessive fee of reinfection and the place individuals who get contaminated don’t get long-term immunity from the illness. It helps perceive the high-level patterns of transmission, the influence of various interventions, and the potential for endemicity (how a illness circulates inside a inhabitants).
The SIS mannequin can be utilized on ailments like:
Limitations of the SIS mannequin
The SIS mannequin has its limitations. This mannequin shouldn’t be relevant to ailments that supply some degree of longer-term immunity after restoration. It doesn’t keep in mind how vaccines could have an effect on illness unfold and assumes that each one people inside a compartment have equal ranges of susceptibility to getting contaminated. In the true world, this state of affairs is unlikely. The SIS mannequin does embody details about components which will have an effect on an infection charges inside a compartment. For instance, age, intercourse, co-morbidities, and different parameters can play a job in how inclined persons are to an infection.
Inhabitants density, socio-economic determinants, behavioral facets, and far more can influence illness unfold and outbreaks. The SIS mannequin can not incorporate these components into its framework.
Key takeaway: The SIS mannequin (Inclined, Contaminated, Inclined) can be utilized to mannequin ailments with a excessive an infection fee. It’s a easy framework that’s simple to make use of and affords a quick, high-level understanding of illness reinfection charges throughout an outbreak. Its limitations are that it doesn’t embody demographic variations, social determinants of well being, inhabitants density, immunity from vaccines, and different components.
