By characterizing the time evolution of COVID-19 in term of its ‘velocity’ (log of the new cases per day) and its rate of variation, or ‘acceleration’, we show that in many countries there has been a deceleration even before lockdowns were issued. This feature, possibly due to the increase of social awareness, can be rationalized by a susceptible-hidden-infected-recovered model introduced by Barnes, in which a hidden (isolated from the virus) compartment H is gradually populated by susceptible people, thus reducing the effectiveness of the virus spreading. By introducing a partial hiding mechanism, for instance due to the impossibility for a fraction of the population to enter the hidden state, we obtain a model that, although still sufficiently simple, faithfully reproduces the different deceleration trends observed in several major countries.

通过用“速度”（每天新病例的日志）及其变化率或“加速度”来表征COVID-19的时间演变，我们表明，即使在锁定之前，许多国家也存在减速被发行。此功能可能是由于社会意识的增强所致，可以通过由Barnes引入的易感隐藏感染恢复模型来合理化，在该模型中，隐藏的（与病毒隔离）隔室H被易感人群逐渐感染，从而降低了病毒传播的效力。通过引入部分隐藏机制，例如由于一小部分人口无法进入隐藏状态，我们获得了一个模型，尽管该模型仍然足够简单，但仍可以忠实地再现在几个主要国家中观察到的不同减速趋势。