The authors are Christopher Avery, William Bossert, Adam Clark, Glenn Ellison, Sara Fisher Ellison, the paper is very good but the abstract is uninformative. Here is one excerpt:
A notable shortcoming of the basic SIR model is that it does not allow for heterogeneity in state frequencies and rate constants. We discuss several different sources of heterogeneity in more detail in Section 2.
The most important and challenging heterogeneity in practice is that individual behavior varies over time. In particular, the spread of disease likely induces individuals to make private decisions to limit contacts with other people. Thus, estimates from scenarios that assume unchecked exponential spread of disease, such as the reported figures from the Imperial College model of 500,000 deaths in the UK and 2.2 million in the United States, do not correspond to the behavioral responses one expects in practice. Further, these gradual increases in “social-distancing” that can be expected over the courses of an epidemic change dynamics in a continuous fashion and thus blur the distinctions between mechanistic and phenomenological models.13 Each type of model can be reasonably well calibrated to an initial period of spread of disease, but further assumptions, often necessarily ad hoc in nature, are needed to extend either type of model to later phases of an epidemic.
I recommend the whole paper.