What Is in the Flu Shot? Here's How Experts Explain Common Ingredients
Remember: the ingredients in your flu vaccine are there to keep you safe from a deadly virus.
The thinking behind this—which isn't entirely incorrect—is because the flu shot itself contains the influenza virus. But not in a way that will make you sick. "The flu shot is made of either killed virus or proteins that are part of the virus, which essentially tricks the immune system into developing a response—namely antibodies to ‘fight off’ the virus,” Tania Elliott, MD, an infectious disease specialist at NYU, tells Health.
In other words: When your body is exposed to either the dead virus or parts of the virus, it (hopefully) learns to fight against the virus, so that if you encounter it, you don't become ill, or you don't become as severely ill as you would without protection.
On that note, it's also important to point out that the flu shot isn't the same general vaccine administered year after year—annually, there are different variations of the flu shot, to pair with the popular circulating viruses. "There are many strains of influenza virus, so, each year, scientists from around the world get together to figure out which strains of flu virus are likely to be circulating that year, and those are the ones put into the flu shot,” Dr. Elliot says.
Some years require more tweaking than others. “In some years, only one strain has to be changed; in others, multiple have to be changed,” Sherif Mossad, MD, an infectious disease expert at Cleveland Clinic, tells Health.
OK, but what else is in the flu shot?
The influenza vaccine doesn't only contain inactive or parts of the flu virus. While there is not one flu shot ingredient list—since multiple flu shots are on offer every year—there are certain flu shot components that you’re likely to see if you look up what’s in the flu shot of your choosing. Below is a list of some of the components of many flu shots.
You’ve likely heard that people with egg allergies can’t or shouldn’t get flu vaccines. The reasoning behind that thinking is that egg protein is found in some flu shots.
While it’s true that there is egg protein in many flu shots—because many flu vaccines are made in chicken eggs—having an egg allergy doesn’t mean you shouldn’t get the flu shot. In fact, the CDC has said that egg allergies shouldn’t keep anyone from getting the flu shot because the amount of egg protein found in the shot is so low it wouldn’t cause an allergic reaction, Waleed Javaid, MD, director of infection prevention and control at Mount Sinai Downtown in New York, tells Health.
That said, if you’re still uncomfortable, you can talk to your pharmacist about getting an egg-free flu shot.
Preservatives, like formaldehyde, are put in some vaccines to keep the mixtures from being contaminated. Dr. Javaid explains that, while it’s reasonable to be concerned when you hear that a substance like formaldehyde is in something you’re getting injected into your body, it’s important to keep the big picture in mind. Namely, the size of the flu shot: 0.5 milliliters. The amount of formaldehyde in a flu shot isn’t enough to hurt you.
While formaldehyde can be dangerous if you, for instance, try to drink a cup of it, it’s not as foreign to your body as you might think: Your digestive tract produces it. If you're still concerned, Dr. Javaid says there are preservative-free options available upon request.
Adjuvants are in some flu shots to illicit a stronger immune response against the influenza virus. In other words—to help your body better flight off the flu, should you come in contact with it.
One adjuvant used in flu shots provided for the 2020-2021 season is called MF59. MF59 is made of squalene, a substance that is naturally found in humans and animals and can help your immune system be better prepared to fight off the flu. Another example of an adjuvant added to some vaccines is aluminum salts, per the CDC.
These are added to vaccines to keep them potent while they’re transported to doctor’s offices and pharmacies and stored. Examples of stabilizers used in vaccinations are sugar and gelatin, per the CDC.
When you think about the reason we use antibiotics in the first place—to kill off bacterial infections—the fact that antibiotics are in the flu shot makes sense. “Antibiotics are in the flu shot so bacteria don’t grow,” Dr. Javaid explains.
If you’re concerned about what’s in your flu shot, you should definitely talk to your doctor and pharmacist about the best option for you, like an egg- or preservative-free option. But at the end of the day, experts warn, it’s important to remember the end goal, which is protection against a deadly virus that kills people of all ages—up to 62,000 Americans in the 2019-2020 season alone, per the CDC—every year.
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