Microbiology 9th Edition by Laura Black, Jacquelyn Black

Exercise 4

Suppose that the health department of city A mounts a suc cessful campaign to get children immunized against measles. Only 100 out of 10,000 children fail to receive the vaccine. Now suppose that city B, the same size as city A, has not carried out a successful measles vaccination program. Of the 10,000 children in city B, 5,000 had measles when the disease last struck the population.
(a) If a child with measles moves to city A, what is the chance that child will encounter a susceptible child?
(b) If a child with measles moves to city B, what is the chance that child will encounter a susceptible child?
(c) Comparing the two scenarios, which city has the higher herd immunity, and in which city is an infected child more likely to transmit the disease to a susceptible child?