Some people who become vaccinated still contract the disease they were vaccinated against. But if most people get vaccinated against a disease, such as measles, then the population achieves “herd immunity,” which means that there are so few cases of the disease that even people for whom vaccinations are ineffective are unlikely to contract the disease. An article in the New York Times responded to this question about the measles vaccine: “If most people are getting vaccinated, why does it matter if I don’t vaccinate my child?”

a. Is “herd immunity” a public good?

b. What does “free riding” mean? Is the parent asking the question attempting to free ride? What will be the effect of this free riding on vaccination rates against measles?

c. Given your answer to part (b), why do most people vaccinate their children against measles, and why do many adults get vaccinated against influenza?