Challenges in control of Covid-19: short doubling time and long delay to effect of interventions

Lorenzo Pellis; Francesca Scarabel; Helena B Stage; Christopher E Overton; Lauren H K Chappell; Katrina A Lythgoe; Elizabeth Fearon; Emma Bennett; Jacob Curran-Sebastian; Rajenki Das; Martyn Fyles; Hugo Lewkowicz; Xiaoxi Pang; Bindu Vekaria; Luke Webb; Thomas A House; Ian Hall

For the estimation of the growth rate, we focus on the number of confirmed cases in European countries that have experienced large local epidemics ( Figure 1A) , as reported by the WHO [28] . To avoid relying only on case confirmation, which could be affected by numerous biases, we also estimate the growth rate in hospitalisations, intensive care unit (ICU) admissions and deaths in Italy ( Figure 1B ; [5] ). To ensure generalisability of results, we performed another analysis on a larger set of European countries ( Figure 2 ). With the exception of a few countries with a small number of cases and potentially unreliable data, we consistently find doubling times of about 3 days or less, that appear to be sustained before mitigation interventions are put in place ( Figure 2 ). These are significantly shorter than early estimates from China [16, 29] . For robustness, we have used two different methods: semiparametric and generalised linear (details in Materials and Methods). Unsurprisingly, the results differ in terms of their confidence intervals, but the conclusions are similar, and are in agreement with the common exploratory analysis based on visually inspecting data plotted on a logarithmic scale ( Figure S3 ).