The effect of non-pharmaceutical interventions on COVID-19 cases, deaths and demand for hospital services in the UK: a modelling study

Nicholas G Davies; Adam J Kucharski; Rosalind M Eggo; Amy Gimma; W. John Edmunds

We assume that the population initially consists of susceptible individuals (S), who become exposed (E) after effective contact with an infectious person. After an incubation period lasting 4 days on average, exposed individuals of age i will develop either a clinical infection with probability , or a subclinical infection with probability . Clinical cases begin with y i 1 y i a preclinical but infectious (I P ) state lasting 1.5 days on average; these individuals then progress to a clinically infected state (I C ), which we assume marks the onset of a clinical case. We assume that subclinical infections (I S ) are half as transmissible as preclinical and clinical infections. Regardless of whether they are clinically or subclinically infected, individuals remain infectious for 5 days on average and are then removed (R) from the infectious state; we assume that removed individuals are immune to reinfection over the 1-2 years over which we simulated the epidemic. Hospitalisations and deaths from COVID-19 are assumed to occur among clinical cases only, and we assume that the clinical outcome of a case does not impact upon transmission dynamics.