Figure 2. The expected number of additional people vaccinated in a vaccination activity per batch of 100 vaccine doses delivered, in a hypothetical population of 1,000 individuals where ρ = 0.8.

If ψ = 0, then each vaccine dose reaches an individual not yet covered by this activity until the entire accessible population is vaccinated (800 individuals in this example). For higher values of ψ, each additional dose delivered into the system has a reduced chance of reaching an individual not yet covered by this activity.