A careful inspection of the cumulative curve of confirmed COVID-19 infections in Italy and in other hard-hit countries reveals three distinct phases: i) an initial exponential growth (unconstrained phase), ii) an algebraic, power-law growth (containment phase), and iii) a relatively slow decay. We propose a parsimonious compartment model based on a time-dependent rate of depletion of the susceptible population that captures all such phases for a plausible range of model parameters. The results suggest an intimate interplay between the growth behavior, the timing and implementation of containment strategies, and the subsequent saturation of the outbreak.

仔细检查意大利和其他受灾国家中已确认的COVID-19感染的累积曲线，发现三个不同的阶段：i）初始指数增长（不受约束的阶段），ii）代数幂律增长（包含阶段） ），以及iii）相对缓慢的衰减。我们根据易感人群的时间依赖性消耗率提出了一个简约隔室模型，该模型捕获了合理范围内的模型参数的所有此类阶段。结果表明，生长行为，遏制策略的时机和实施以及随后爆发的爆发之间存在密切的相互作用。