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

The highlighted risks of underestimating the combination of short doubling times and long delays between infection and case detection are consistent with the now-common pattern of countries misjudging the initial small number of observed cases, only to realise the storm has already arrived. At unconstrained growth, even the immense effort of doubling local hospital capacity only buys 3 days of reprieve before bed capacity is breached. Being blind to the extent of an epidemic and the true number of infections at any one time results in intervention strategies based on the number of observed cases and measurements of R 0 . For COVID-19, these are insufficient and dangerously underestimate the true degree of intervention required to slow down and bring the epidemic under control. We advocate stronger action from national and international health care communities, with a particular focus on supporting lowand middle-income countries where numbers of cases, at the time of writing, appear to be relatively low. In settings where health care capacity is low and intergenerational mixing common, swift action will save numerous lives. Note that the Italian Hospitalised and ICU cases are daily prevalence rather than daily incidence.