The advantage of assessing interventions with respect to R or q is that a considerable amount of community structure can be incorporated into the models with moderate effort. It is, of course, also necessary to look at the calendar-time dynamics of any local epidemic, if it occurs, and we do so in Section 5.6 with an appropriate model. A small step in this direction is possible with the model underlying our calculations for R and q. While this underlying model contains some community structure, it ignores the depletion in the number of susceptible individuals as the epidemic progresses. The latter is of no concern for the calculation of R and q. In terms of number infected, this model can trace the transmission adequately only during the early stages of the outbreak. In Figure 5.5 we depict the way different interventions affect the mean rate of growth over the first four generations.
Figure 5.5(a) gives the mean of the total number of cases over 4 generations. From Figure 5.5(b), one can deduce that the ‘default AVs’ strategy reduces the number of cases within 4 generations by approximately half, and that by providing AVs prophylactically to 40% of an at-risk group within the population leads to a reduction in the number of cases of between 80% and 90%. Such a reduction would infer a significant reduction in the demand on the health care system.
Figure 5.5 Effect of various antiviral strategies on the early spread, for different values of R0 and ƒ=0.8.
- TI, the mean of the total number of cases after 4 generations
- Z, the proportion by which the mean number of infectives within 4 generations is reduced, compared with the case of no intervention.