Method. The next-generation method, developed by Diekmann et al. [8] and Diekmann and Heesterbeek [9] , and popularised by van den Driessche and Watmough [10] , is a generalisation of the Jacobian method. It is significantly easier to use than Jacobian-based methods, since it only requires the infection states (such as the exposed class, the infected class and the asymptomatically infected class) and ignores all other states (such as susceptible and recovered individuals). This keeps the size of the matrices relatively manageable.