Comparison of different exit scenarios from the lock-down for COVID-19 epidemic in the UK and assessing uncertainty of the predictions

Anatoly Zhigljavsky; Roger Whitaker; Ivan Fesenko; Yakov Kremnitzer; Jack Noonan

The reproductive number R 0 is the main parameter defining the speed of development of an epidemic. There is no true value for R 0 as it varies in different parts of the UK (and the world). In particular, in rural areas one would expect a considerably lower value of R 0 than in London. Authors of [3] suggest R 0 = 2.2 and R 0 = 2.4 as typical; the authors of [4] use values for R 0 in the range [2.25, 2.75]. We shall use the value R 0 = 2.5 as typical, which, in view of the recent data, looks to be a rather high (pessimistic) choice overall. However, R 0 = 2.5 seems to be an adequate choice for the mega-cities where the epidemics develop faster and may lead to more causalities. In rural areas, in small towns, and everywhere else where social contacts are less intense, the epidemic is milder. The flow-chart in Figure 1 describes the process of illness. We assume that the person becomes infected τ I days after catching the virus, where τ I has Poisson distribution with mean of λ I days. Parameter λ I defines the mean of the incubation period during which the person cannot spread the virus. Recommended value for λ I is λ I = 5.