Most reactions simply mean the vaccine is doing its job.
No, the flu shot doesn’t give you the flu, doctors insist. But 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, MD, 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 nose and go on with their lives, while others stay home with a fever, and still others develop a cough. It’s the same with the flu shot, says Claudia Vicetti, MD, 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.
Here’s how your body may react after the flu shot, when you should and shouldn’t worry, and how to feel better once side effects hit.
Common flu shot side effects
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
- Redness or swelling at the injection site
- Low-grade fever
- Coughing or sneezing (with the nasal flu vaccine)
Yes your arm might be sore or uncomfortable after getting the shot, but it’s usually “one day of discomfort,” Dr. Vicetti says, “and not everybody gets that [side effect].”
As for redness and swelling at the injection site? That’s actually a good thing, she says, because it means your immune system is responding to the vaccine. Dr. Kemmerly would agree: “Their immune system is raring to go and they’re making antibodies.”
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,” Dr. Kemmerly notes, “but for the most part people feel pretty good.”
However, there are people who do develop serious side effects after getting the flu vaccine, such as allergic reactions or 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.)
⚠️ Talk to your doctor if your flu shot side effects persist. If someone has breathing problems or other serious signs of an allergic reaction after getting a flu vaccine, treat it as a medical emergency and seek help ASAP.
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.
So why do some people feel like the flu shot gives them the flu?
If you’re feeling crummy for days after getting your flu vaccine, something else may be going on. Oftentimes, people delay getting a flu shot until flu season is in full swing, Dr. 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.
Other times, people wrongly blame the flu shot for their symptoms when, in fact, they’re 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).
Another thing you have to know: “The flu” isn’t a single virus. Each year 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, says the Centers for Disease Control and Prevention (CDC).
And, while the flu vaccine works well in the young and healthy, older folks with weaker immune systems may not make sufficient levels of antibodies to fend off the flu, the CDC notes. People over age 65 should talk to a doctor about getting a “high-dose” flu vaccine, sometimes called a “senior” flu vaccine. It contains four times as much flu antigen as the standard 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 crummy. 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, Dr. Kemmerly says. All in all, minor aches are a small price to pay for the vast protection the flu vaccine provides—wouldn’t you rather feel a little headachy than ill-and-bedridden for a week or longer?