We built an epidemiological model where people adopt protective behaviours due to fear of contracting an infectious disease. These adaptive behaviours are assumed to lower an individual’s risk of infection. We analyzed dynamics of this model as well as the effects of fear on three important public health metrics: outbreak length, epidemic final size, and peak prevalence.
The coupled dynamics of fear- and disease-spread are rich and can lead to counter-intuitive results. In particular, it is not always the case that more effective protective behaviours lead to the most favourable population-level outcomes; intermediate levels of effectiveness are optimal in some cases. This result depends on when fearful individuals become infected with respect to the main outbreak that is mostly driven by the infection of non-fearful individuals.