The effective reproduction number, < eff , is the average number of secondary cases produced by a typical infectious individual Effective Reproduction Number, < con , for surgical masks. Notice that < con decreases as a higher percentage of people wear masks as well as when masks are more effective. However, < con is not greatly reduced even when 50% of the population wears masks and masks are 50% effective. doi:10.1371/journal.pone.0009018.t006