If humans were perfectly logical creatures, we’d all get flu shots. They are easy to find, usually free, and undeniably effective. In the 2016-2017 flu season alone, they prevented an estimated 5.3 million cases of the flu. Yet less than half of Americans get the shot, proof positive of the enduring irrationality of our species.

Some of that gap is due to misinformation. But rejection of the flu shot is about more than just celebrity retweets of bad science about vaccines in general. In many ways, the flu shot violates our understanding of how medicine works in ways that tickle the irrational parts of our brains.

For example, people expect medicine to make them feel better. So minor side effects are usually ignored, since most medicine is taken when you already feel lousy. But not the flu shot. You get it when you’re feeling healthy, and it makes some people feel a little sick.

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The side effects aren’t huge: Some people have pain at the injection site or a sore arm. But because that means going from feeling good to feeling bad, the brain associates the shot with illness and tries to convince you not to do that again. That’s sensible in an instinctual way, but flawed in any rational sense.

This is made worse by the fact that even though side effects are rare, occurring in about 1 in 100 shots, they’re not rare enough. Humans like certainty and stability. We want a shot that we react to the same way each and every time, not one that exists in a “maybe” state.

By itself, a 1 percent chance of having a reaction to the flu shot isn’t too bad. But you need to get the shot every year, making it likely that somewhere in your circle of family and friends, it will make someone feel a bit sick each year. And because of something called the availability heuristic, the vivid story of someone you know getting a little bit sick looms large and makes you think it is much more common than it actually is.

The flu shot falls short of the predictability we crave in another way: It isn’t 100 percent effective, at least not in the way people generally think of vaccine effectiveness. You can get a flu shot and still get the flu. And the vaccine’s effectiveness varies from year to year, as does the formulation, so uncertainty piles on uncertainty. Having been conditioned to stable medicines like aspirin, which have been around and relatively unchanged since antiquity, the flu shot feels new and unstable by comparison.

The flu shot also requires us to inhabit what psychologists call a counterfactual world. Say you got a flu shot last year and didn’t get the flu. Would you have gotten sick if you hadn’t got the shot? It’s hard to know: You would have been more likely to have gotten the flu, but that’s not the same thing.

Choosing to get a flu shot requires projecting a future state in which you are sick, recognizing how bad it would feel, and then taking action to avoid that future state. That’s no small feat of mental gymnastics, especially when it is likely that you’ve had at least some years during which you didn’t get the flu shot and didn’t get the flu. Humans are notoriously bad at affective forecasting — accurately imagining what you will feel like in the future — and doing it for the flu shot is no exception.

Even though flu shots are available at many pharmacies and workplaces, and are free with insurance plans, the psychological factors add up and take their toll, contributing to the relatively low percentage of Americans who get a yearly flu shot.

But we don’t have to be prisoners to our irrational instincts. One of the great things about being human is that we can override our natural tendencies. So let’s try a bit of what psychologists call frame-shifting.

Did you get the sniffles around the same time as a flu shot? You may have had a case of the common cold, which the flu shot does not protect against, or any one of dozens of other respiratory diseases that tend to happen around the same time as the flu season. Or you really did get a light case of the flu, because you were already exposed before getting the shot or shortly after; the flu shot can take up to two weeks to become fully effective.

Worried the vaccine isn’t 100 percent effective? It actually is: It always minimizes the chance that you’ll get the flu, but also makes the flu dramatically less serious if you do get it, converting a weeklong nightmare into a few hours of nausea. The flu vaccine always works, if “works” means minimizing the overall effects of the flu.

Don’t like that the formula changes? Think of it as an upgrade. The reason the vaccine varies from year to year is that experts are constantly monitoring what strains of the flu virus might be coming down the pike, and they are getting better at predicting which combination we need each year. This is the iShot X, better than ever.

Can’t imagine what it’s like to get the flu? Don’t bother trying. Just consider the following: Everyone gets the flu from someone else. If you get vaccinated against it, you are less likely to give the virus to someone else, like a child or older adult, who can die from the infection.

That’s the most important reframing. Humans are communal creatures: We care deeply about protecting each other. If everyone who gets the flu got the virus from someone else, that means we have a chance to keep others safe by getting flu shots. The more people who get the shot, the greater the herd immunity, which is just fancy science talk for a simple reality: If there is no one around who can get the flu, it doesn’t spread. Check out this GIF to see how it works.

Think about someone you love: a child or a grandparent or a pregnant woman. Now imagine how you’d feel if you accidentally give them the flu and they end up in the hospital — or dead.

Our irrational brains can work both ways. In the same way that feelings of uncertainty can make you avoid the flu shot, feelings of love can help you get one.

So even if you feel healthy, even if it hurts a little, even if you get a sore throat, even it isn’t perfect, getting a flu shot every year is worth it. Flu shots save lives.

Be better than your brain. If you love someone, get a flu shot.

Matt Wallaert is a behavioral scientist who serves as chief behavioral officer at Clover Health, a Medicare Advantage plan.

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  • Explain this to me. I have never had the flu shoot worked and been around people who had the flu yet I never got sick with the flu.I did catch a 24 hour cold gone the next morning. And I’m 38 Why should i get the flu shoot and risk catching the flu?

    • DJ vaccines are a massive money market and they will create just about any vaccine to treat any illness so they can take your hard-earned money. They could give a shit less about what they actually put in those to preserve their shelf lives for YEARS. they’ve even got a multi-billion-dollar vaccine court that awards people with vaccine injuries. To presume you can target a specific flu illness every single year when there are thousands of different ones is absolutely preposterous, laughable…

  • This is just causing more variants and longer flu seasons, the targeted groups get short term immunity and everyone will just get it more. Thanks for being more interested in money than reason (statistical trickery). The masses have no idea whats going on. Good luck!

  • The flu shot has always worked for me and I’m 35. If I don’t get it, usually I’m fine but on two separate years I did catch it and it was awful. The first time I ended up in er with trouble breathing and had to buy Tamiflu. Second time I ended up with both ears infected and snot coming out of my eyes. Had to pay for two doctor visits and antibiotics. It’s just so much cheaper and safer to get the shot. It’s very cheap at Costco.

  • “In the 2016-2017 flu season alone, they prevented an estimated 5.3 millioncases of the flu. Yet less than half of Americans get the shot”

    There’s 325 million people in America. Half of that is 162.5 million. And due to those 162.5 million vaccinations, 5.3 million cases of the flu were prevented. 5.3 million out of 162.5 is only 3.2%

    3.2%! That doesn’t even cover the margin of error! The flu vaccine is literally useless, statistically equal to a placebo!

  • Another stupid article, downplaying or ignoring the marketing that led to this willful ignorance. The Flu Shot works, and these injection have saved millions of lives and billions of dollars. The complimentary and alternative medicine advertisers peddle lies, in order to market their pseudo sconce. They along with physicians, and medical providers present stupidity as a choice. Americans in general are greedy and selfish, the people who ‘choose” not to get a flu shot lack intelligence and empathy. Why else would they choose to spread the flue to sick people, children or the elderly, who end up hospitalized or dead.
    None of the “Alternative Medicine Quacks” are going to explain the facts, not when they can sell some vitamins, hocus pocus or a short massage, and pretend they healed someone. in Alternate fact America, even the facts are a choice!

  • This is one of the dumbest articles I’ve ever read. Sure, please inject me with chicken DNA, formaldehyde, aluminum, gelatin, antibiotics, polysorbate 80, and the worst of all, MERCURY. The most toxic substance ever! NO THANKS. Take your junk science elsewhere.

  • So many Pinocchio’s, Matt. No, the flu shot isn’t 100 percent effective and responsiveness declines significantly as people age. Yet older people are the ones most led to believe the flu shot will keep them well. Check out the CDC’s stats on A(H3N2) in older adults.

    Furthermore, when did you ever have a case of flu that consisted of “a few hours of nausea”? That’s what happens after you run a marathon.

    And really, people don’t get flu shots because they’re irrational morons? Ad hominem attacks really don’t bolster your argument.

    Finally, you neglected to mention the most important way to keep from getting and spreading the flu: handwahing.

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