Growth rate and acceleration analysis of the COVID-19 pandemic reveals the effect of public health measures in real time

Yuri Tani Utsunomiya; Adam Taiti Harth Utsunomiya; Rafaela Beatriz Pintor Torrecilha; Silvana Cassia Paulan; Marco Milanesi; Jose Fernando Garcia

Using MR and HMM on ECDC data frozen on April 2 nd 2020, we evaluated the utility of the framework in identifying countries reaching deceleration or stationary growth. We also looked for countries presenting complex arrangements of the five growth stages. The countries found to have reached a near-stationary stage at some point were China and South Korea (Figure 1b-c) . By projecting official government announcements against the fitted curves of these countries, we observed that decline in growth acceleration occurred shortly after the implementation of measures that drastically reduced human movement. Deceleration of growth was achieved within 2 weeks and the prevalence plateaued within 6 weeks. These results indicated that: (i) the effect of public health measures on SARS-CoV-2 prevention can be detected in seemingly real time by monitoring the behavior of acceleration curves; and (ii) restriction to human mobility is very effective in controlling the spread of the disease, but takes several weeks to produce a stationary growth. These findings are in line with a recent study showing that human mobility explained early growth and decline of new cases of COVID-19 in China (14) . As discussed before, one should not immediately assume that a country in stationary growth will remain in that stage, since acceleration could take off again if new cases are imported or preventive measures are relaxed. In fact, our HMM classifier categorized the apparent stationary growth stage of China and South Korea as a linear growth. Indeed, both countries have not reached a perfect asymptote and their COVID-19 prevalences are instead growing in a linear pattern.