Most reactions simply mean the vaccine is doing its job.
As a runner, your goal is to always stay in tip-top shape—whether it’s preventing a pesky injury from sidelining you or warding off an illness like a cold or the flu. And, since flu season has arrived, getting your flu shot is an important step in being able to run your best throughout the winter months.
But one question crops up every year: Can the flu shot make you sick? No, doctors insist. However, it does pose potential side effects, just like any other vaccine or medicine. Your arm might be tender after your flu shot, or your child could develop a cough after getting a dose of the nasal flu vaccine.
“The majority of patients really don’t have any side effects,” says Sandra Kemmerly, M.D., system medical director for hospital quality at Ochsner Health System in New Orleans. And when symptoms do occur, they’re usually mild and clear up in a day or two, she says.
So why do some people feel sick after the flu shot while others don’t? Doctors say reactions to the flu vaccine differ from person to person and that multiple factors are likely at play.
Think about how people respond to the common cold. Some folks get a runny noseand go on with their lives, while others stay home with a fever or develop a cough. It’s the same with the flu shot, says Claudia Vicetti, M.D., a pediatric infectious disease specialist with UnityPoint Health in Cedar Falls, Iowa. “You’re stimulating your body, and your immune system may react in different ways,” she says.
Plus, minor side effects are nothing compared to how dangerous the flu actually can be. During last year’s season, up to 62,000 people died due to flu complications between October 2019 and April 2020, according to preliminary estimates from the Centers for Disease Control and Prevention (CDC).
That’s why it’s so important to get vaccinated every year. “The flu” isn’t a single virus. Each season, a new vaccine is developed to match circulating strains. Getting a flu vaccine can protect you against the same or related viruses in the vaccine, but it won’t cover every possible strain that a person might encounter, the CDC explains. This year’s vaccine will target the following strains:
- A/Guangdong-Maonan/SWL1536/2019 (H1N1)pdm09-like virus
- A/Hong Kong/2671/2019 (H3N2)-like virus
- B/Washington/02/2019 (B/Victoria lineage)-like virus
Even though it is not 100 percent effective, getting a flu shot is the best way to protect yourself from getting sick, and can significantly lower your chances of winding up in the hospital. It is important to get vaccinated before the end of October, so your body has time to build up immunity—especially this year, as the novel coronavirus and influenza circulate at the same time. The CDC says it is “more important than ever” this season to protect yourself from the flu, which can help reduce the strain on healthcare systems that are responding to the COVID-19 pandemic.
Once you do get the vaccine, you may be one of the rare few that feels a bit crummy afterward, but it shouldn’t last very long. Here are the flu shot side effects to know, when you should and shouldn’t worry, and how to feel better once side effects hit.
What are the side effects of the flu vaccine?
Whether you get a flu shot or the spray-mist type, side effects are generally no big deal. You may experience the following:
✔️Soreness or aching in your arm
Your arm might be sore or uncomfortable after getting the shot, but this is a good thing: It means your immune system is responding to the vaccine and creating antibodies, says Dr. Kemmerly. Plus, it’s usually “one day of discomfort,” Vicetti adds, “and not everybody gets that [side effect].”
✔️Redness, pain, or swelling at the injection site
This is another good sign that your immune system is raring to go and responding to the vaccine properly, Kemmerly says. Plus, any time something breaks the skin barrier (like a needle), it may get red and swollen as your body reacts to it as a foreign object. This side effects is common and should only last a few days.
Experiencing a low-grade fever (below 101 degrees) after the flu shot is possible, but it’s not very common. If it’s any higher than that, you may already be sick with another virus that commonly circulates during flu season. A person might catch a cold, for example, or RSV (respiratory syncytial virus, a common childhood illness).
Oftentimes, people delay getting a flu shot until flu season is in full swing, Kemmerly points out. They were already “incubating” the flu virus and “then, lo and behold, they got the flu—but totally unrelated to the flu shot,” she says.
✔️Nausea, headaches, or fatigue
These are all totally normal reactions as your body responds to the flu vaccine, the CDC says.
✔️Dizziness or fainting
Like any other vaccine, some people may experience dizziness or fainting after getting a flu shot, but this has much more to do with the process—getting a needle poked into your arm—than the vaccine itself, the CDC says. The organization emphasizes that nearly all vaccines receive reports of people fainting afterward, so it’s not unique to the flu shot alone.
✔️Coughing or sneezing
The nasal flu vaccine, the type your child might get if he or she doesn’t have asthma or a recent history of wheezing, can cause some of the same side effects as the flu shot—minus the sore arm—plus some additional ones. “There can be some coughing and sneezing,” Kemmerly notes, “but for the most part people feel pretty good.”
While the flu shot is unlikely to give you a sore throat, the CDC says that you may experience this side effect with the nasal flu vaccine. If you happen to experience this side effect, it will usually happen soon after you get vaccinated and be mild and short-lived.
There are people who do develop serious side effects after getting the flu vaccine, including Guillain-Barré syndrome (GBS), a neurologic condition that attacks your body’s nerve cells, in turn causing muscle weakness or paralysis in severe cases. (These people fall on the list of people who should not get a flu shot.) Before you freak out, know that this condition is extremely rare. In fact, for every 1 million flu shots given, only one or two of those people will develop GBS, the CDC states.
There are people who may experience an allergic reaction to the flu vaccine or its components, such as gelatin, antibiotics, or other ingredients. The CDC says that signs of a severe allergic reaction can include difficulty breathing, wheezing, swelling around the eyes or lips, hives, high fever, and a fast heartbeat.
Life-threatening reactions to the flu shot are extremely rare. “I’ve been practicing for 30 years. I’ve never seen an anaphylactic reaction to the flu shot,” says Kemmerly. Still, talk to your doctor if your side effects persist. If someone has signs of an allergic reaction after getting a flu vaccine, treat it as a medical emergency and seek help ASAP.
⚠️ If you’ve had a life-threatening allergic reaction to the flu shot in the past, you should not get the vaccine.
If you have an egg allergy, you can still get vaccinated, the CDC says, but it should be done in a controlled setting where you can be monitored. In this case, talk to your doctor about your egg allergy so you can both make an informed decision about your vaccine.
How to treat flu shot side effects
Usually, any side effects you might get from the flu vaccine go away on their own within a day or two—but you don’t have to tough it out if you really feel run down. Try these self-care measures to feel better ASAP:
For muscle aches, headache, or flu-like symptoms, take a pain reliever, such as Tylenol or ibuprofen.
For arm pain after the flu shot, apply a cool compress.
The same goes for side effects of the nasal flu vaccine. Treatment is based on a person’s symptoms, Kemmerly says. All in all, minor aches are a small price to pay for the vast protection the flu vaccine provides for both you and those around you.
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