Fast spread of COVID-19 in Europe and the US and its implications: even modest public health goals require comprehensive intervention

Ruian Ke; Steven Sanche; Ethan Romero-Severson; Nicholas Hengartner

First, with the global efforts to develop vaccines for COVID-19, it is important to have an 266 accurate measure of the basic reproductive number, R0, to set the threshold level of herd 267 immunity needed to prevent transmission. Previously, R0 for COVID-19 were estimated to be 268 between 2-3 2-5 and were widely reported in official documents 18 and public media. These 269 estimates are mostly based on an epidemic growth rate between 0·1 and 0·14/day 2-5 , which we 270 now know to be inconsistent with many new lines of evidence and data as discussed in this paper 271 and a previous work 6 . The growth rates that we estimated in this paper are simply not consistent 272 with a low R0. Previously we showed that with a mean serial interval, defined as the duration of 273 time between onset of symptoms in an index case and a secondary case, of 6-9 days 3,19 and an 274 epidemic growth rate between 0·19-0·29/day, the value of R0 must be higher than 3 6 . Using the 275 same framework as in Ref. 6, we find that when the growth rate is 0·19/day, the median R0 is 276 . CC-BY-NC-ND 4.0 International license It is made available under a author/funder, who has granted medRxiv a license to display the preprint in perpetuity.