Ring Vaccination and Smallpox Control
Figure 5. The effective reproduction number Rυ, that determines the success of intervention is shown as a function of the basic reproduction number R0 for a vaccination coverage of 50% in the casual contact ring. In A, contacts are not monitored after vaccination; in B, all identified contacts are isolated and cause not further transmission. The different lines in A are for different assumptions about how long it takes to trace and vaccinate those contacts. In B, it does not make a difference whether it takes 1, 2, or 3 days to find the contacts. If R0 is 5, the intervention will be successful in both cases, if R0 is 10, 50% coverage is no longer sufficient any longer to curb the epidemic.