In the mid-1970s, only 25 percent of the country's elderly were vaccinated; the current rate is 65 percent. Yet over that same period, total U.S. flu deaths rose 400 percent. The main reason is that the elderly population as a whole—those 65 and over—grew 52 percent and the "elderly elderly"—people 85 and over—doubled. The very old are particularly unresponsive to vaccine and particularly likely to die from the flu: An 85-year-old, for example, is 16 times as likely to die as a 65-year-old.