This paper shows that the growth behavior of the COVID-19 epidemic in mainland China can be explained as a direct consequence of containment policies that effectively depleted the susceptible population.

In Mainland China, confirmed cases increased from approx. 330 on Jan. 21st, 2020 to more than 17,000 on Feb. 2nd, 2020 in a matter of two weeks. An initial exponential growth of confirmed cases is generically expected for an uncontrolled outbreak. In contrast, the recent outbreak of COVID-19 in Mainland China was characterized by a distinctive subexponential increase of confirmed cases during the early phase of the epidemic.

The authors of this paper introduce a parsimonious model that captures both quarantine of symptomatic infected individuals as well as population-wide isolation practices in response to containment policies or behavioral changes.

Their model captures the observed growth behavior accurately, and therefore has implications for the careful implementation of containment strategies for ongoing secondary outbreaks of COVID-19 or similar future outbreaks of other emergent infectious diseases.