Fig. 1: Illustration of the integrated mathematical model.
From: Equitable access to COVID-19 vaccines makes a life-saving difference to all countries
a, The multistrain model. A linear strain space and local movement by a one-direction stepwise mutation are considered. M denotes the number of possible strains; μm denotes the mutation probability per infection. b, The SVEIRD model. Susceptible individuals (S) become vaccinated (V) at a vaccination rate determined by the global vaccine allocation strategy. Vaccinated individuals become susceptible after losing vaccinal immunity. Exposed individuals (\({E}_{m}^{S}\) and \({E}_{m}^{V}\)) are those infected by strain m and are divided into two classes, either with or without vaccinal immunity. Exposed individuals first become infectious (\({I}_{m}^{S}\) and \({I}_{m}^{V}\)) and then transition to either the recovered state (R) or the deceased state (D). For simplicity, we assume that co-infection is not possible and recovered individuals are immune to the disease. c, The SVEIRD-based metapopulation model. Due to travel restrictions, infectious and deceased individuals do not move between countries.
