No test is better than a bad test"": Impact of diagnostic uncertainty in mass testing on the spread of Covid-19

Nicholas Gray; Dominic Calleja; Alex Wimbush; Enrique Miralles-Dolz; Ander Gray; Marco De-Angelis; Elfride Derrer-Merk; Bright Uchenna Oparaji; Vladimir Stepanov; Louis Clearkin; Scott Ferson

SIR models offer one approach to explore infection dynamics, and the prevalence of a communicable disease. In the generic SIR model, there are S people susceptible to the illness, I people infected, and R people who are recovered with immunity. The infected people are able to infect susceptible people at rate β and they recover from the disease at rate γ [28] . Once infected persons have recovered from the disease they are unable to become infected again or infect others. This may be because they now have immunity to the disease or because they have unfortunately died. Figure 8 shows a schematic of the generic model formulation, and how people move between the states. Figure 9 demonstrates the typical disease dynamics, the Infected corresponding to the now well known curve that we are trying to flatten. The SIR model has two ways in which the number of new infections falls to zero. Either the number of susceptible people reduces to a point at which the disease can no longer propagate, perhaps because of a vaccine or natural immunity, or the epidemic stops if the basic reproduction rate of the disease falls below 1 due to social distancing or effective viral suppression.