You probably heard about the Disneyland measles outbreak last year. One infected person is thought to have visited the theme park, and thanks in part to low immunization rates, 142 people in California and six other states got sick. It wasn’t close to the worst recent measles outbreak in the United States, but because of its origin in the shadow of Cinderella’s castle, it produced a crescendo of media and public concern about the larger problem of childhood vaccination rates, which have dipped slightly in some states. The discussion around vaccine reluctance has been growing for years, amplified by the chorus of celebrities and politicians who’ve weighed in, and the childhood vaccination problem has been the primary focus of public health officials in charge of vaccine programs for more than a decade.

But by any imaginable metric, resistance to childhood vaccination is hardly the most worrisome category of vaccination reluctance in the United States. Yes, hundreds of children are getting sick from measles or dying of pertussis (whooping cough) in communities where vaccine refusal has allowed what should have been isolated cases to spread. It’s tragic and infuriating. But it is nowhere near the health threat Americans face because of the astoundingly low number of people getting vaccinated each year against the flu.

The Centers for Disease Control and Prevention estimates that since the 1970s, influenza has killed between 3,000 and 49,000 people each year, most of whom were 65 or older. An average of 200,000 people per year get so sick they have to be hospitalized, including 20,000 children under 5, whose immune systems haven’t fully developed. In 2011-2012, the latest flu season for which the CDC has firm numbers, the illness killed 37 kids under 18. It killed 122 children the season before and 348 during the 2009-2010 H1N1 pandemic.

This public service announcement by the Centers for Disease Control and Prevention highlights the importance of flu vaccines. (CDC)

These figures dwarf the stats for measles and pertussis. The CDC recorded 222 cases of measles in America in 2011, 120 in people 19 or younger. Nobody died. 2012 was a record year for pertussis, with 48,277 cases and 20 deaths, 18 of those in children.

The health and economic costs of influenza are staggering. Five to 20 percent of the U.S. population gets the flu every year. A 2007 analysis in the journal Vaccine reported: “Based on 2003 US population, we estimated that annual influenza epidemics resulted in an average of 610,660 life-years lost, . . . 3.1 million hospitalized days, and 31.4 million outpatient visits. Direct medical costs averaged $10.4 billion . . . annually. Projected lost earnings due to illness and loss of life amounted to $16.3 billion . . . annually. The total economic burden of annual influenza epidemics using projected statistical life values amounted to $87.1 billion.” (Population growth since 2003 suggests that these numbers are roughly 10 percent higher now.)

The CDC recommends an annual flu vaccination for anyone 6 months and older. Herd immunity for flu — which means enough people are vaccinated so that if one person gets sick, the disease can’t spread — would be achieved if roughly 80 percent of us were inoculated. There isn’t a single age group that meets those targets. The CDC estimates flu vaccination rates of 67 percent for adults 65 and older, 47 percent for people 50 to 64, 34 percent for those 18 to 49, and 59 percent for kids 17 and under.

If the risk is so high, why are these vaccination rates so low? In short, because facts alone don’t determine how we feel about a risk. The affective, emotional nature of risk perception is such that we sometimes worry more than the evidence warrants — parents overly concerned about the health risks of childhood vaccines, for instance — and we sometimes don’t worry as much as the evidence warns. When it comes to the flu, people aren’t nearly as worried as the facts suggest they should be.

In one study of adults who didn’t get the flu vaccine, 28 percent of respondents said, “I don’t need it,” and 16 percent said, “I didn’t get around to it” — essentially, they weren’t worried enough. Fourteen percent said, “I don’t believe in flu vaccines,” even though in most years, the vaccine reduces your chance of getting sick by more than half. Another 14 percent said, “I might get the flu from the vaccine.” (Like the association between childhood vaccines and autism, this common myth is incorrect.) Five percent said, “I dislike needles,” even though the vaccine now comes in nasal-spray form. And 3 percent said, “No vaccine was available,” which is stunning, since tens of millions of doses are prepared each year and millions of doses are thrown away unused at the end of every flu season.

Studies of the psychology of risk perception by Paul Slovic and others have found that we worry much more about risks to kids than risks to adults, and we worry much less about risks with which we’ve grown familiar, such as the regular seasonal flu. What worries us more prompts more widespread and more passionate advocacy, including more media attention. Together those factors raise pressure on the government to respond to what we’re most afraid of, even though what we fear more might not be what threatens us the most.

That’s why we need better programs to increase flu vaccination rates, including improved public education and communication about risks. We should also consider requiring vaccination for health-care workers and for other workers who physically interact with the public; economic incentives, such as discounts on health insurance similar to those already offered to nonsmokers or people who join a gym; and disincentives, such as higher out-of-pocket doctor’s visit fees for those who choose not to vaccinate.

Such programs would undoubtedly be cost effective. They certainly would protect public health, and children’s health, far more than efforts to increase childhood vaccination rates for other diseases (work that should continue, of course). A CDC report in December 2014 found that if flu vaccination levels had reached the government’s target of 70 percent during the 2013-2014 flu season, 5.9 million illnesses and 42,000 flu-related hospitalizations could have been avoided.

National Influenza Vaccination Week, an annual CDC observance to draw attention to the importance of flu vaccination, came and went in December with no fanfare, even though tens of thousands of us are getting sick or dying from influenza. These illnesses and deaths could be dramatically reduced if we had the right priorities — and if we all simply got our flu shots.

Correction: An earlier version of this story incorrectly stated the flu vaccine’s efficacy rate in a typical year.