When you get a flu shot, this is what happens to your body

Getting the flu shot is important. After all, influenza is no joke. Not to be confused with the stomach "flu," the virus targets your respiratory system, wreaking havoc on your lungs, throat, and nose. It can cause a variety of symptoms, including fatigue, congestion, aches and chills, a fever, headache, and more. Additionally, complications can include bronchitis, pneumonia, ear infections, heart problems, and even death in some cases. In short, it's nothing that anyone wants to experience.

Despite the risks and potential financial fallout that the flu can cause, only about 40 percent of Americans get their flu shot every year, according to the CDC. That's an alarmingly low number, especially since the vaccine is available at a relatively low cost at many pharmacies and medical establishments.

Part of the reason so few people are immunized against influenza may be due to misconceptions about the vaccine, according to Harvard Medical School. So just what is it that happens to your body when you get the flu shot, according to solid scientific evidence? Read on to find out. 

Who should definitely get a flu shot?

You might be tempted to skip the flu shot for a variety of reasons: you've never had the flu, you're not around sick people, you're young and healthy, you're planning on washing your hands and drinking orange juice to prevent getting sick, etc. Or perhaps you don't bother getting it because you don't think it's effective enough, so why waste your time?

But according to the CDC, getting the flu shot is super important for most people. As per their guidelines (via NPR), "anyone and everyone 6 months old and older in the United States should get vaccinated each and every year." That means even if you've never had the flu in your entire life, you should still get immunized against influenza.

It's especially important for more vulnerable populations to get a flu shot, such as people over the age of 65, anyone with an underlying medical issue like asthma or diabetes, and anyone who is pregnant. It's the only way to truly protect yourself against the very real threat of the flu.

This is who should not get a flu shot

The CDC generally recommends that anyone over the age of six months gets vaccinated against influenza in order to be as prepared as possible for flu season. However, there are a few exceptions to that rule of thumb, as, for some folks, the vaccine could have adverse effects.

For one, no one under the age of six months should be vaccinated against the flu as they're just too young. Additionally, anyone who has a severe, life-threatening allergy to any of the ingredients in the vaccine, such as antibodies, gelatin, or any other ingredient, shouldn't get a flu shot. The caveat is that if you have an egg allergy, talk to your doctor, as they'll know best if the vaccine will be safe for you. And if you've ever had Guillain-Barré Syndrome, you should consult your doctor as well.

Finally, if you're not feeling well, talk to your healthcare professional, as they may want you to wait until you're healthy before you get vaccinated.

If you're pregnant, you'll protect your baby by getting a flu shot

Since children under the age of six months shouldn't receive a flu vaccine, you might be tempted to think that if you're pregnant, you should abstain from immunizing in order to protect your baby. But as it turns out, the exact opposite is true, as the CDC urges anyone who's pregnant to get the flu shot to ensure the health of the mother and the unborn child.

If you're still worried that the flu shot isn't good for a fetus, fear not: It's totally safe, according to Dr. Alicia Fry, chief of the epidemiology and prevention branch of the CDC's Influenza Division. "I think some of the fears about safety are certainly understandable, but they're misinformed," she explained in an interview with NPR. "[The vaccine] can prevent 70 percent of the illness associated with flu viruses in the baby," she shared. "So it's a double protection: Mom is protected, and the baby's protected." Sounds like a win-win!

Additionally, pregnant women who get the flu shot are 40 percent less likely to land in the hospital with the flu.

About two weeks after the flu shot, you'll be protected from the flu

While the flu vaccine does a decent job of decreasing your chances of getting the flu (and rendering it less severe if you do), it's not instantly effective. Rather, according to Dr. Tanaya Bhowmick, an infectious disease expert at Rutgers Robert Wood Johnson Medical School, it takes some time for the vaccine to be processed by the immune system. "People should realize the vaccine takes two weeks to be effective, so they still could contract the flu during this period," Bhowmick shared in an interview with My Central Jersey. "The vaccine exposes your body to a weakened form of the virus, which allows you to mount an immune response." So make sure you plan accordingly for maximum benefit.

Additionally, once you've built up your immunity to influenza via the vaccine, you'll be protected for approximately six months. That's usually sufficient to keep you healthy throughout the duration of the flu season, though you need to get the flu shot every year.

You're more likely to stay out of the hospital if you get a flu shot

Even if you get the flu shot, there's still a chance that you can get the flu, which honestly is a bit frustrating. But until we have access to a more perfect vaccine that targets the influenza virus with more precision, the current vaccine formula is the best we have.

Additionally, there are still some very significant benefits afforded by the flu vaccine in its current form. For one, it makes you less likely to get the flu, of course, which in and of itself is pretty fantastic. Plus, according to a 2017 study in the journal Clinical Infectious Diseases, you're less likely to land in the hospital with the flu than if you weren't vaccinated. And if you do wind up in the hospital with the flu, you're less likely to be admitted to the ICU and will have a shorter length of stay than folks who forgot to get their flu shot. This was again confirmed in a 2018 study in the journal Vaccine. That's some good news!

You might feel a prick when you get the flu shot

Let's face it: Getting an injection is never fun. Even when you have the most deft hand wielding the syringe, it can still be an anxiety-inducing experience. That's especially the case for folks who have trypanophobia, or a fear of needles, which can be extremely intense for both children and adults with the condition. 

But according to Dr. Stacey Gorski, a biology professor at University of Sciences, getting a flu shot is still better than coming down with a nasty case of the flu. "I don't like needles either," she confessed in an interview with Delaware Online. "But for what you are gaining for those second or two of discomfort I think is well worth it."

If you really can't stomach the idea of getting an injection but still want to be vaccinated, you may be able to receive the vaccine via nasal spray. Talk to your doctor to see if this is an option for you, and if it will afford you the right protections.

Your arm might turn red and swell after getting a flu shot

One of the most common side effects from receiving the flu shot is redness, tenderness, soreness, and swelling at the injection site, according to the CDC. While it is temporary in that it will only last for a few days, it can be quite uncomfortable, especially if you use your arms a lot in your daily life. No one likes having a sore arm!

Fortunately, there are actions you can take in order to minimize the reaction you'll have to the flu shot, according to Dr. Ali Raja, executive vice chairman for the department of emergency medicine at Massachusetts General Hospital. "If you find that you usually have a sore arm after the flu shot, it's not at all inappropriate to take acetaminophen or ibuprofen to help with that," he explained in an interview with The Boston Globe. He also noted that some folks place a hot pack on the injection site, which can decrease pain and relax the muscle. So don't let that stop you from getting immunized. 

You might feel under the weather after getting a flu shot

It's not uncommon to feel under the weather when you're vaccinated against influenza. But according to Libby Richards, an associate professor of nursing at Purdue University, that's actually a good sign. "When you receive the flu shot, your body recognizes the inactive flu virus as a foreign invader," she penned in an article in The Conversation. "This is not dangerous; it causes your immune system to develop antibodies to attack the flu virus when exposed in the future." 

So while this is indeed brought on by getting the flu shot, it's still not a bad thing, as it's helping you develop immunity against the flu. "This natural immune response may cause some people to develop a low-grade fever, headache or overall muscle aches," she continued. "These side effects ... are likely the body's normal response to vaccination."

So while getting sick is never fun, the reaction you have to the flu vaccine is significantly less severe that catching the flu itself.

You might feel a little dizzy and achy after getting the flu shot

A swollen arm and an immune reaction aren't the only side effects you'll deal with after being vaccinated against influenza. Unfortunately, there are other unpleasant things you may have to endure, though none of them are as bad as the flu by a long shot.

For one, you might find that you're experiencing aches and pains in various muscles in your body, according to Healthline. This reaction will usually happen on your first day, and fortunately will abate in two days or less. If this happens to you, ask your doctor if it's safe to take an over-the-counter pain reliever to mitigate any discomfort.

Additionally, it's possible that you might experience dizziness after getting the flu shot, and you might even faint. If that's been the case for you before, be sure you inform the person administering the injection so they can plan accordingly. Making sure to have a snack before getting vaccinated and planning to sit down for a while afterwards may help you reduce any adverse effects. 

Severe side effects are extremely rare after getting the flu shot

Before discussing any serious side effects that can happen after getting the flu shot, it's important to note how uncommon they are. They're so rare, in fact, that according to Dr. Eve Switzer, an Oklahoma-based pediatrician, they've never been a problem for her. "Having been in clinical pediatric practice for over 20 years personally giving the flu vaccine to my patients, I have yet to see or hear about any severe complications from my patients," she told The List. "Typical concerns reported by patents are mild in nature and include sore limbs and fever/fussiness." That's good news!

That said, according to Healthline, the serious side effects can include: high fever (higher than 101 degrees Fahrenheit), severe allergic reactions (with symptoms such as hives, trouble breathing, dizziness, weakness, swelling, and an elevated heart rate), and Guillain-Barré syndrome. If any of these symptoms happen to you, it's important to contact your doctor right away.

You'll become part of the herd after getting the flu shot

Getting the flu shot isn't just about protecting yourself from the influenza virus, although that in and of itself is extremely important. Literally no one wants to be laid up with a bad case of the flu for weeks on end, or, worse yet, landing in the hospital because of it!

But in addition to protecting yourself, you're protecting the people around when you when get a flu shot, according to Dr. Michael Brady, associate medical director at Nationwide Children's Hospital. "The whole principle is if you give a vaccine to somebody, you protect them from getting infected, but you also prevent them from transmitting the disease to other people," he explained in an interview with Web MD. This is called herd immunity, or community immunity: the more people that are protected from a disease, the less it will be spread.

This is especially important for people with compromised immune systems who can't get vaccinated, such as folks with cancer or HIV, as well as babies too young to get a flu shot; they rely on herd immunity to stay healthy.

You won't get the flu from the flu shot

There's an awful lot of misinformation floating around out there about the flu shot and about vaccines in general. And according to Libby Richards, an associate professor of nursing at Purdue University, one misconception in particular is responsible for people skipping out on the influenza vaccine. "One of the common myths that leads people to avoid the flu shot is that they think the shot will give them the flu," she wrote in an article in The Conversation. "But that is simply not true. The virus in the vaccine is not active, and an inactive virus cannot transmit disease." Therefore, it's physically impossible to get the flu from the flu shot.

So why is it that some people feel sick after getting their influenza vaccine? "What is true is that you may feel the effects of your body mounting an immune response," she continued. "But that does not mean you have the flu." Myth busted!

You won't be exposed to mercury when you get the flu shot

Another misconception about flu vaccines (and vaccines in general) is that they contain dangerous amounts of harmful mercury. Mercury, which is a naturally occurring element, is extremely bad for your health should you be exposed to it, according to the World Health Organization. That's why it's important to be mindful about the amount of seafood you eat, as some fish and shellfish contain methylmercury, a compound you don't want to consume in excess.

But when it comes to what's found in vaccines like the flu shot, there's nothing to be alarmed about, as vaccines do not contain methylmercury, according to the CDC. They do contain a mercury-based preservative called thimerosal, which contains ethylmercury — but that's different than methylmercury. Ethylmercury is cleared from your body much faster than methylmercury, and therefore isn't going to cause your body any harm. Multiple studies confirm this, so there really isn't anything to stress about when it comes to mercury and vaccines.

As always, if you have concerns, talk to your doctor.

Here's what else won't happen to your body when you get the flu shot

The misinformation that circulates about vaccines doesn't stop with worries about the flu shot causing the flu or exposing people to mercury, either. Unfortunately, the rise of the anti-vaccination movement has caused more and more people to avoid getting vaccinated and vaccinating their children, according to an article in The New York Times. That's because folks are afraid that vaccines will cause a number of complications, including autism, lung problems, seizures, SIDS, and more. That can be a scary prospect for anyone!

But according to the U.S. Department of Health and Human Services, vaccines, including the flu vaccine, have been found to be overwhelmingly safe and effective. They have been rigorously studied and closely monitored for many years, and have been shown to prevent a variety of serious diseases. Of course, there are people out there who continue to insist that vaccines are dangerous, but the science just doesn't support that notion.

So when it comes to your flu shot, if you have any hesitations, talk to your doctor.