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

We model a susceptible-infectious-recovered framework (SIRf) [6] to simulate the spread of SARS-CoV-2. The population is separated into those currently contributing to transmission (y, equation 1 ) and those not available for infection (z, equation 2 ). Cumulative death counts ( , equation 3 ) are obtained by considering that mortality occurs with probability , on a Λ θ proportion of the population that is at risk of severe disease ( ) among those already ρ exposed (z); we consider the delay between the time of infection and of death ( ) as a ψ combination of incubation period and time to death after onset of symptoms. The small proportion of the population that is at risk of severe disease ( ) is an aggregate model ρ parameter, taking into consideration both a potentially lower risk of infection than the rest of the population, as well as the actual risk of severe disease.