The next-generation method is likely the most frequently used method to calculate R 0 . It has been used extensively to calculate R 0 -like values from host-vector models (see Wonham et al. [11] , Gaff et al. [12] or Gubbins et al. [13] ). However, it does not produce the number of newly infected individuals in the same infection class and does not always produce the average number of secondary infections.