Despite common perceptions, it’s not just the elderly and frail who are at significant risk of a life-threatening complication. Data from China suggest that many chronic health problems increase the likelihood of a bad outcome, including cardiovascular disease, which affects nearly half the adults in the United States in some form, and diabetes, which affects about 10 percent. In Italy, 99 percent of the fatalities were people with pre-existing medical problems, especially hypertension.

Moreover, in the United States, obesity-related metabolic conditions may put the public at exceptional risk. Today, more than two of three adults have high body weight, and 42 percent have obesity, among the highest rates in the world. Almost two in 10 children have obesity. Excessive weight, and the poor-quality diet that causes it, is strongly associated with insulin resistance, chronic inflammation and other abnormalities that may lower immunity to viral respiratory infection or predispose to complications.

In a California study of the 2009 influenza pandemic, people with obesity were twice as likely to be hospitalized compared with the state population.