It’s shaping up to be a bad flu season that is peaking early, sending large numbers of people to hospitals, and even killing healthy teenagers.

Still, despite universal recommendations by public health officials urging just about everyone over the age of six months to get vaccinated, most Americans don’t get the flu shot.

As of November, only 35 percent of American adults and 40 percent of kids had been vaccinated against the flu, according to the Centers for Disease Control and Prevention, and those numbers are pretty typical for an average year. Even among pregnant women, who are a high-risk group, a recent report found that compliance rates are only about 50 percent.

The reasons why the majority of people fail to line up for flu shots, even in pandemic years, are varied, complicated and differ from person to person, experts say. Driven by misinformation, some fear that the vaccine caries risks. Others are simply lazy. Some think the flu shot is unnecessary or won’t do any good.

As the public drags its feet, researchers are busy trying to figure out how best to convince people to seek out an annual shot in the arm or spray in the nose. One of the biggest barriers is that it’s hard to get people’s attention with public health messages.

“You pitch the influenza vaccine as a way to maintain health, that the healthy thing to do is get vaccinated, but if you really wanted people to get it then you should tell them it would make them better looking or have more sexual appeal,” said John Treanor, chief of the infectious diseases division at the University of Rochester Medical Center in New York.

“Only some people see health as a motivator,” he said. “It’s not obvious how to get young people to get vaccinated.”

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Each year, influenza viruses sicken hundreds of thousands of Americans and kill between 3,000 and 49,000 of them, according to the CDC.

The best way to reduce your chances of succumbing the virus is to get the vaccine, either as a shot or nasal spray. Neither form is 100 percent effective, which means it’s still possible to get the flu after being vaccinated. But, Treanor said, there is good evidence to support the theory that higher rates of vaccination prevent more illnesses.

Several studies, for example, have found significantly lower rates of flu among unvaccinated adults in communities where large proportions of schoolchildren have been vaccinated compared to communities where kids don’t get the shot.

According to some estimates, Treanor said, 60 to 70 percent of people or more would need to get vaccinated to produce true herd immunity and really prevent the spread of influenza through a community. Compliance rates are rarely that high, even among health-care workers.

To better understand why some people regularly seek out vaccines while others consistently fail to act, one team of researchers created a virtual online world that simulated flu outbreaks.

Over a period of 45 days, about 50 people played the online game, which gave players daily information about how bad the situation was and how many people had fallen ill. Every day, participants received points for staying healthy and lost points for getting sick.

Players could spend points to take protective measures that would reduce their risk of infection, or they could hold on to their points and hope for the best. At the end of the game, they received a gift card, whose value was determined by the number of points they had managed to keep.

The points that could be spent to gain protection in the game represented the kinds of intangible costs that might prevent people from getting vaccinated in the real world – things like a fear of needles, worries about side effects, the time and effort needed to get to the clinic or even the money required to get a shot.

Throughout the simulation, individuals dealt with risks of infection in very different ways, the team reported recently in the journal PLoS One. Some people were particularly risk-averse and took any chance they could get to protect themselves, while others always rolled the dice with their health, choosing to hold on to as many points as they could.

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There were ways to influence people’s behavior, though. Personal experiences made a difference, for one thing. So if players were infected early on in the game, they became more likely to get virtual flu shots for the rest of the simulation.

As more people were reported to be infected, players also became more likely to want to spend points to improve their chances of staying healthy. That finding suggests that it might help to keep the public better informed about how widespread the flu is each year, before it has reached crisis proportions, said Frederick Chen, an economic epidemiologist at Wake Forest University in Winston-Salem, North Carolina.

Another way to increase the number of people who paid the price to stay healthy, the study found, was to reduce the cost of protection.

“The idea that cost matters tells us that when it comes to promoting flu shots, we have to think about how we can reduce costs, and that doesn’t just mean monetary costs,” Chen said. “If we can make it more accessible or easier for people to get to flu-shot clinics, or if you’re a company, maybe you can give time off to workers to get flu shots – anything to make life easier would help.”

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That includes battling fears by assuring people that side effects are minimal or non-existent and that the flu shot won’t make them sick or increase their chances of getting sick.

Because different people responded so differently to the costs and benefits presented to them in the study, it’s clear that one public health approach will not be equally effective for all, Chen. For at least some people, though, it might help to appeal to their altruistic side.

Public health officials may need to work harder, for instance, “to make people realize that when you get the flu shot, you’re not just benefiting your self but you’re benefiting other people as well,” Chen said. “You’re one less person who can infect other people. If we emphasize that — that you are not just helping yourself but helping the community — I think for some people, that might increase the perceived benefit of getting the flu shot.”

Photo: Flu vaccine. Credit: iStockPhoto