Ask Dr. Dave: Can You Get the Flu From a Flu Shot?

Flu season is coming up, and some of you might be avoiding getting a flu shot because you think it will give you the flu. In short, you can’t get the flu from a flu shot.

So how come in the past you got the flu, even though you got a flu shot?

Two things: Maybe you didn’t get the flu, and instead it was one of those nasty cold viruses like our friend the rhinovirus, which we discussed in a previous post. Or, you did get the flu, but it was from getting the flu, not the vaccine.

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The flu vaccine usually bats about .650 each season; that is, it protects you from getting the flu about two-thirds of the time. Compare that to the measles vaccine, which protects you 99 percent of the time! We can’t all be as perfect as the measles vaccine. That’s a seriously sweet vaccine.

Anyway, back to the flu vaccine. Why is it not quite as badass as other vaccines? Because the flu is one badass virus. Flu, short for influenza, has the ability to mutate in two lethal ways.

One way is when it combines with a totally different flu to make a super-flu, and the other way is when it mutates some of its protective coat to create the same old flu in a different disguise. The former happens every few decades and causes a worldwide pandemic (think bird flu) and the other happens every year and causes epidemics (think seasonal flu).

So now, put yourself in the minds of the vaccine scientists. Your job is to build a vaccine for a virus that changes at least every single year…and then people still get mad when you only protect them more than half the time! How do they even do that well?

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Months before a flu season begins, the world’s vaccine scientists collect strains of the flu from all over the world. The U.S. scientists mainly collect samples down in the Southern Hemisphere since people are fresh off their winter of cuddling and sneezing on each other.

The scientists kill the viruses they figure will be the Big Deal to make an injectable vaccine, and they take out the dangerous parts of these viruses to make the inhaled nasal virus (approved for most needlephobes aged 2 through 49).

For most people who get the vaccine, it is spot on. The vaccine potentially saves millions of lives each year. And despite the fact that vaccines are made from killed or mutated viruses, they do not cause the flu.

So what’s the bottom line? Allow me to use an armor metaphor, since armor metaphors are back in style thanks to HBO’s Game of Thrones. If you had the choice between wearing no armor and armor that covered two-thirds of your body, what would you do?

Of course, you’d choose the armor. I guess I should have prefaced that by saying enemies are shooting arrows at you or something. You smart folks would wear the armor, and you’d still try to dodge the arrows.

And remember—even if you get the flu vaccine, if someone sneezes on you, please wash your hands before sticking them in your mouth. Safety first.

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Dave Margolius is a physician in San Francisco, California. He is originally from Cleveland, Ohio, and attended Brown University for undergrad and med school. He is currently doing his residency in internal medicine at UCSF. His main interests are in health policy, improving primary care, and healthcare for all.