Figure 4. Epidemic curves for each age group and combined total for pandemic (H1N1) 2009 with an initial average uncontrolled effective reproduction number, ${\mathfrak{R}}_{\text{unc}}^{\text{avg}}=1.3$, in which N95 respirators are worn by 10% of the population and are 20% effective in reducing susceptibility and 50% effective in reducing infectivity.

In this case, waves are produced because the intervention strategy is temporarily halted and restarted, e.g., if the number of infectious individuals drops below 30,200 reported cases, people stop wearing masks. Once the number of infectious individuals reaches 30,200 cases people start to wear masks again. Note that in this scenario the epidemic never dies out and the number of infectious individuals continues to oscillate between 29,400 and 32,500.