You have 100 doses of a vaccine against a deadly strain of influenza that is sweeping the country, with no prospect of obtaining more. Standing in line are 100 schoolchildren and 100 elderly people.
The elderly are more likely to die if they catch the flu. But they also have fewer years left to live and don't get out enough to easily spread or catch the disease. The kids are more likely to act like little Typhoid Marys, sneezing virus over anyone they encounter, and have almost their whole life ahead of them. But they're also less likely to die if they get sick.
Whom do you vaccinate?
Plus, there's this: "Last year, scientists showed in a model that if you vaccinate about 60% of U.S. schoolchildren, flu deaths among the elderly would fall to 6,600 from the typical 34,000."
As a parent, it's easy to convince me that the nation's schools are the key reservoir of infectious disease.