Fundamental principles of epidemic spread highlight the immediate need for large-scale serological surveys to assess the stage of the SARS-CoV-2 epidemic

Jose Lourenco; Robert Paton; Mahan Ghafari; Moritz Kraemer; Craig Thompson; Peter Simmonds; Paul Klenerman; Sunetra Gupta

population at risk being distributed around 1%. The model output (posterior) for time of introduction (the start of transmission) place this event a couple of days after the first confirmed case in the country, and over a month before the first confirmed death ( Figures 1E-F) . In both R 0 scenarios, by the time the first death was reported (05/03/2020), thousands of individuals (~0.08%) would have already been infected with the virus (as also suggested by [5] ). By 19/03/2020, approximately 36% (R 0 =2.25) and 40% (R 0 =2.75) of the population would have already been exposed to SARS-CoV-2. Running the same model with R 0 =2.25 and the proportion of the population at risk of severe disease being distributed around 0.1%, places the start of transmission at 4 days prior to first case detection and 38 days before the first confirmed death and suggests that 68% would have been infected by 19/03/2020. The results of the same exercise for Italy ( Figure 2 ) place the time of introduction around 10 days before the first confirmed case, and around a month before the first confirmed death (Figures 2E-F) when the proportion of the population at risk of severe disease is around 1%. By 06/03/2020, approximately 45 days post introduction, the model suggests that approximately 60% (R 0 = 2.25) and 64% (R 0 = 2.75) of the population would have already been exposed to SARS-CoV-2. When the proportion of the population at risk is around 0.1%, the start of transmission is likely to have occurred 17 days prior to first case detection and 38 days before the first confirmed death with 80% already infected by 06/03/2020.