Flu shots work, and are a smart way to reduce the chances that you’ll end up sick this winter. But that’s not the impression you might get if you listen to the rumor mill. Flu shot myths abound, and it’s time to put the biggest ones to rest.

Myth: The Flu Shot Doesn’t Work

The flu vaccine isn’t perfect, but you’re still better off getting it than not. In a good year, the flu vaccine is about 70 percent effective; if we’re unlucky, the rate can dip lower.

Two years ago, the shot was only 23 percent effective. Last year’s did better,around 60 percent. The exact rate depends on which strains of flu are circulating in your area, but most years the effectiveness hovers around 50 percent.

Think of it this way: if somebody coughs on you during flu season, wouldn’t you like to have a coin-flip chance of escaping unharmed? Fifty percent is a lot better than zero. The Centers for Disease Control and Prevention (CDC)summarizes: “Influenza vaccination, even when effectiveness is reduced, can prevent thousands of hospitalizations.”

Why are flu shots often ineffective? Other vaccines have better track records: the measles vaccine is 97 percent effective, for example, in children who get both of the recommended doses. Here are a few reasons that make flu vaccine a weird one.
  • There isn’t just one flu. Flu viruses mutate a lot, so we need a new shot every year. The people who make flu shots have to choose in the spring which strains should go in the shot for that fall and winter, and if they guess wrong, the shot will be less effective. (That’s what happened in 2014, the 23 percent effectiveness year.)
  • Some people don’t respond well to the vaccine. Flu shots are less effectivein children under age 2, and adults over 65. Other factors and health conditions can affect how well you’ll respond.

Because effectiveness varies so much, scientists including those at the CDC keep tabs on what strains of flu are circulating and how the vaccine currently fares against them. When they change their recommendations, it can look like a flip-flop, but they’re really just staying on top of the best available information.

For example, the nasal spray version of the flu vaccine isn’t recommended this year. (Sad trombone for kids and really everyone who hates needles.) Back in 2002-2005, the spray worked so well in children that it was recommended over the shot. But last year, the spray’s effectiveness was just 3 percent, versus 63 percent for the shot. So the recommendation keeps up with what we currently know.

Myth: I Don’t Need a Flu Shot

Depending on the year, between five and 20 percent of people get the flu each year in the US. The people at greatest risk of getting sick or dying from the flu are young children, the elderly, and people with underlying health problems. But healthy people are just less likely to get seriously ill; they’re not invincible.

Flu symptoms can include fever, cough, and sore throat, so they’re similar to the symptoms of colds and other less serious illnesses. That means plenty of people think they’ve had the flu when really they’ve had something else. Ask anyone who’s had a confirmed case of influenza: flu knocks you on your ass, with fatigue and achiness that last a week or more.

And, not to get too morbid, but people really do die from the flu. The number of deaths can be anywhere between 3,300 to 49,000 per year. For comparison, around 30,000 people die in car crashes. There’s another important reason to get a flu shot, even if you’re healthy. Every person who is susceptible to the flu is a stepping stone the virus can use to reach the elderly and sick. Those people are the most vulnerable to flucomplications like pneumonia—and the most likely to die from flu.

Myth: The Flu Shot Can Give You the Flu

This is a persistent myth, and it’s just plain wrong. The flu shot given through a needle (the only kind that’s recommended this year) contains viruses that are either inactivated (“dead”) or chopped into pieces.

You get flu from live viruses. There are no live viruses in the flu shot.

The nasal spray did contain live viruses, but they were weakened versions that cannot survive in the lungs. In rare cases they could make people sick with a mild flu-like illness, but they still could not cause full-blown flu.

I know some folks reading this will swear that they, or someone they know,totally got the flu from the flu shot once. But remember, we tend tomisremember and misunderstand our own experiences. You may remember getting sick, figure that was “the flu”, and blame the flu shot you got. You may also have gotten the actual flu, and blamed the shot for giving it to you rather than remembering the shot is only partially effective.

If you got a flu shot, and then came down with a case of the definite actual flu, here’s what may have happened:

  •  Maybe the shot didn’t work for you, that time. Like we said above, it’s not perfect.
  • Maybe you got very mild flu-like symptoms after the shot. This isn’t common but it happens—and it’s not the actual flu. Remember, flu tends to be pretty long-lasting and severe. A fever or cough that results from the flu shot won’t last more than a day or so.
  • Maybe you didn’t get the shot soon enough. You’re not fully protected until two weeks after you get the shot, so it’s possible to catch the flu in the meantime.

Overall, side effects from the flu shot are minimal to nonexistent for most people. If there’s a reason the shot might be risky for you, your doctor or the person who administers your shot will be able to discuss this with you. For example, infants under six months and people with life-threatening allergies to ingredients of the vaccine should not get the shot. It’s recommended for almost everyone else.

Myth: It’s Not the Right Time

September might seem too early to get a flu shot, since the disease isn’t really circulating yet. But remember, if you wait to get the shot until everyone you know is getting sick, you might get infected before the vaccine has a chance to take effect.

Only some people should wait: specifically, anyone over age 65. Elderly people’s immunity fades after three or four months, and peak flu season can occur as late as March. The Advisory Committee on Immunization Practices(ACIP) says that it’s better to get the shot whenever you can; you wouldn’t want to delay and then end up forgetting to get it at all. But if you’re over 65 and know you can stick to a schedule, getting a shot in November would be ideal. Either way, consider asking for the high dose vaccine that is designed specifically for older folks.

The rest of us should get the shot as soon as it’s convenient. If you forget, though, and find that everyone around you is getting sick in January, you should still go ahead and get the shot then. It will still protect you for however much of the flu season remains.

Illustration by Sam Woolley.