Crowding and the epidemic intensity of COVID-19 transmission

Benjamin Rader; Samuel Scarpino; Anjalika Nande; Alison Hill; Benjamin Dalziel; Robert Reiner; David Pigott; Bernardo Gutierrez; Munik Shrestha; John Brownstein; Marcia Castro; Huaiyu Tian; Bryan Grenfell; Oliver Pybus; Jessica Metcalf; Moritz U.G. Kraemer

across China during most of the time captured by our study and certainly after January 23, 2020 2 . If social 182 distancing reduces non-household contacts by the same relative amount in all prefectures, there will be 183 more contacts remaining in crowded areas, since baseline contact rates are higher. In this case, it may take 184 much longer for the infection to die out post-intervention in crowded areas (Figure 4D ), leading to a 185 lower intensity outbreak with larger final size, as seen in our data ( Figure 1C) . 186 187 . CC-BY 4.0 International license It is made available under a author/funder, who has granted medRxiv a license to display the preprint in perpetuity. epidemics across the world. Crowded cities tend to be more prolonged due to increased crowding and the 201 higher potential for transmission chains to persist (i.e., in denser environments there is higher potential for 202 two randomly selected hosts in a population to attain spatiotemporal proximity sufficient for COVID-19 203 transmission). Indeed, that epidemic intensity is higher in comparatively low density areas is consistent 204 with observations in the most affected areas in Italy (e.g., Bergamo) 32 . Our findings confirm previous 205 work on epidemic intensity of transmission of influenza in cities 9 albeit by a different mechanism: 206 . CC-BY 4.0 International license It is made available under a author/funder, who has granted medRxiv a license to display the preprint in perpetuity.