A Little Side-Story..

I was just reading my Econ textbook when I came across, "Note that this problem is similar to a person deciding whether to be vaccinated against an illness....even though the patient bears the full cost of the vaccination, many of the resulting benefits accrue to others. Thus, the extra benefit from any one person being vaccinated is that others also become less likely to contract the illness." I'm supposed to be learning about the Cost/Benefit principle... but all I can think is "herd immunity!!"