Sorry for the delayed response.
The assumptions and raw data are explained on Page 4 as follows:
We modified an individual-based simulation model developed to support pandemic influenza planning (5,6) to explore scenarios for COVID-19 in GB. The basic structure of the model remains as previously published.
Note: here are the references:
5. Ferguson NM, Cummings DAT, Fraser C, Cajka JC, Cooley PC, Burke DS. Strategies for mitigating an influenza pandemic. Nature 2006;442(7101):448–52.
6. Halloran ME, Ferguson NM, Eubank S, et al. Modeling targeted layered containment of an influenza pandemic in the United States. Proc Natl Acad Sci U S A 2008;105(12):4639–44
Further, from the Imperial College paper, the rest of the assumptions:
We assumed an incubation period of 5.1 days9,10. Infectiousness is assumed to occur from 12 hours prior to the onset of symptoms for those that are symptomatic and from 4.6 days after infection in those that are asymptomatic with an infectiousness profile over time that results in a 6.5-day mean generation time. Based on fits to the early growth-rate of the epidemic in Wuhan10,11, we make a baseline assumption that R0=2.4 but examine values between 2.0 and 2.6. We assume that symptomatic individuals are 50% more infectious than asymptomatic individuals. Individual infectiousness is assumed to be variable, described by a gamma distribution with mean 1 and shape parameter =0.25. On recovery from infection, individuals are assumed to be immune to re-infection in the short term. Evidence from the Flu Watch cohort study suggests that re-infection with the same strain of seasonal circulating coronavirus is highly unlikely in the same or following season (Prof Andrew Hayward, personal communication). Infection was assumed to be seeded in each country at an exponentially growing rate (with a doubling time of 5 days) from early January 2020, with the rate of seeding being calibrated to give local epidemics which reproduced the observed cumulative number of deaths in GB or the US seen by 14th March 2020.
My note: I think these are reasonable. Doubling time of 5 days may actually be somewhat optimistic - we are currently doubling every 2 to 3 days in the incidence rate here in the US.
Hope that helps.
nwrep, it certainly does help! It is exactly the information I was seeking. THANK YOU!