Covasim: An agent-based model of COVID-19 dynamics and interventions
Table 2
Age-linked disease susceptibility, progression, and mortality probabilities.
Key: rsus: relative susceptibility to infection; psym: probability of developing symptoms; psev: probability of developing severe symptoms (i.e., sufficient to justify hospitalization); pcri: probability of developing into a critical case (i.e., sufficient to require ICU); pdea: probability of death (i.e., infection fatality ratio). Relative susceptibility values are derived from odds ratios presented in Zhang et al. [47]. Mortality rates are based on O’Driscoll et al. [48] for ages <90 and Brazeau et al. [49] for ages >90. All other values are derived from Verity et al. [45] and Ferguson et al. [50], which did not differentiate 80–89 and 90+. Values were validated from model fits to data on numbers of cases, numbers of people hospitalized and in intensive care, and numbers of deaths from Washington and Oregon states. Note that "overall" values depend on the age structure of the population being modeled. For a population like the USA or UK, the symptomatic proportion is roughly 70%, while for populations skewed towards younger ages, this proportion is lower. Similarly, overall mortality rates are estimated to vary from 0.2% in Kenya to 0.9% in the USA and 1.4% in Italy.