Climate affects global patterns of COVID-19 early outbreak dynamics

Gentile Francesco Ficetola; Diego Rubolini

Host-pathogen interaction dynamics can be significantly affected by environmental conditions, either directly, via e.g. improved pathogen transmission rates, or indirectly, by affecting host susceptibility to pathogen attacks (1). In the case of directly transmitted diseases, such as human influenza, multiple environmental parameters such as local temperatures and humidity impact on 5 virus survival and transmission, with significant consequences for the seasonal and geographic patterns of outbreaks (2) (3) (4) (5) (6) . A recently discovered coronavirus, SARS-CoV-2, is the aethiological agent of a pandemic disease, Covid-19, causing severe pneumonia outbreaks at the global scale (7) . Covid-19 cases are now reported in about 170 countries and regions worldwide (8) . Three months after the discovery of SARS-CoV-2, the global pattern and the early dynamics of Covid-10 19 outbreaks seem highly variable. Some countries have been experiencing limited growth and spread of Covid-19 cases, while others are suffering widespread community transmission and nearly exponential growth of infections (8) . Understanding the drivers of early growth rates is pivotal to predict progresses of disease outbreaks in the absence of containment measures (9, 10), yet no study has so far assessed the role of environmental variation in the worldwide growth of 15 Covid-19 cases. Given the impact of environmental conditions on the transmission of many pathogens, we tested the hypothesis that the severity of Covid-19 outbreaks across the globe is affected by spatial variation of key environmental factors, such as temperature, air humidity (5, (11) (12) (13) (14) (15) , and pollution [fine particulate matter (16); see methods]. We then evaluated if this could help to illustrate global variation in the risk of severe Covid-19 outbreaks in the coming months. 20 Relying on a publicly available global dataset (8), we computed the daily growth rates r of confirmed Covid-19 cases (Covid-19 growth rate hereafter) for 121 countries/regions (see the Methods section). We limited our measure of epidemics growth rate to the first 5 days after . 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.