8 Common Flu Shot Side Effects and How to Relieve Them
Key takeaways:
The flu shot typically causes mild side effects, such as pain where you received your vaccination and headaches.
Flu shot side effects should go away within 1 to 2 days. If side effects last longer than this, reach out to a healthcare professional.
Most flu shot side effects can be managed at home with over-the-counter pain relievers. Serious side effects are very rare.
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The end of the summer is usually marked by a few things: back-to-school shopping, Labor Day festivities, and advertisements to get your annual flu shot. The term “flu shot” is often used to refer to all flu vaccines. The makeup of the flu vaccine, though, changes each year. These changes help protect us better since influenza strains mutate (change) over time. That’s why it’s recommended to get a flu vaccine every year.
The benefits of getting vaccinated against influenza (the flu) outweigh the risks for most people. But that doesn’t mean it’s free of side effects.
Flu shot side effects at a glance
Below is a list of common and rare side effects of the flu shot. Keep in mind that for this article, when we use the words “flu shot,” we’re referring to injectable flu vaccines. FluMist is a flu vaccine that comes as a nasal spray. FluMist has different side effects than injectable flu vaccines.
Most flu shot side effects are mild and fast-passing. Those discussed below likely won’t come as a surprise if you’ve gotten a flu shot in the past. But keep in mind that many people don’t experience any side effects after their flu shot.
Common flu shot side effects include:
Pain, redness, or swelling at the injection site
Fatigue
Muscle aches
Headache
Nausea
Low grade fever
Rare flu shot side effects and risks include:
Fainting
Severe allergic reaction
Febrile seizures in children
Guillain-Barré Syndrome
1. Pain, swelling, or redness where you received your shot
Pain in the injection area is common with most vaccines. This is especially true for vaccines like the flu shot, which are injected into a muscle (intramuscular injections). Redness and swelling at the injection site is also possible.
This happens because your immune system typically responds to anything that injures the skin or muscle tissue. This is part of our natural healing process. In this case, it’s also a sign your immune system is responding to the flu shot.
Injection site reactions should go away after a day or two in most cases. In the meantime, you can try a warm or cold compress or take an over-the-counter (OTC) pain reliever if the pain is bothersome. But you shouldn’t take a pain reliever before you receive your flu shot. It could interfere with how well the flu shot works.
It’s not common, but if the injection isn’t given properly, it can cause an infection or other problems at the injection site. So if your pain or swelling becomes severe or doesn’t go away, contact a healthcare professional. Seek emergency care if symptoms seem life-threatening.
Good to know: If you’re concerned about the side effects of an injectable vaccine, talk to a healthcare professional about whether FluMist (the nasal flu vaccine) is an option for you.
2. Muscle aches
Muscle aches are another common flu shot side effect. They often happen around the area where you received the shot. But they can also be more widespread.
Does the flu vaccine work? Physicians detail how flu vaccinations work and why they’re beneficial for everyone.
Is the flu vaccine a live virus? Most flu vaccines are inactivated (dead virus) vaccines. Read more pharmacist-backed answers to common flu vaccine questions.
All about FluMist: Read about the nasal spray flu vaccine and who’s eligible to receive it.
Muscle aches are also a common symptom of the flu. So this flu shot side effect may cause some confusion, leading you to think that the shot gave you the flu. But rest assured that this isn’t possible. Muscle aches from the vaccine are simply a sign it’s working and your immune system is responding properly. They’re typically mild and usually go away within 1 to 2 days after vaccination.
3. Headache
Similar to muscle aches, you may develop a headache after getting a flu shot. This is generally mild for most people. It should resolve within a few days of getting the vaccine.
A cool compress on your forehead or an OTC pain reliever may help relieve a headache if needed. Staying hydrated can also help.
4. Feeling like you’re getting sick
As your immune system starts responding to the flu shot, you may experience body-wide side effects. These can include a low-grade fever, nausea, and a general feeling of discomfort.
While not fun, mild flu-like symptoms that appear shortly after your vaccine mean that your immune system is learning from the flu shot. As mentioned, these side effects don’t mean that you’ve caught the flu from the flu shot. The virus that’s in the flu shot is inactivated (not alive or active). So it can’t replicate in your body or cause the flu.
If these symptoms don’t resolve after a few days, seek medical care. It’s possible you were exposed to the flu before you received your vaccine. A healthcare professional can help determine the cause of your symptoms and the best course of action.
5. Fainting or dizziness
Feeling dizzy or fainting is a possible side effect with many vaccines. It’s not very common with the flu shot, but still possible. Feeling faint could also be caused by the process of getting an injection or a fear of needles.
Some reports suggest that fainting after a vaccine may be more common in adolescents than younger kids or adults. But it’s difficult to determine just how often it happens.
While fainting isn’t harmful, falls caused by fainting can be. To help prevent injuries, the healthcare professional giving your vaccine will likely ask you to sit down during your injection. They’ll also ask you to stick around for 15 minutes or so afterward to make sure you’re steady on your feet before you leave. Let them know ahead of time if you have a history of fainting after vaccines. This can help them take extra steps to secure your safety.
6. Allergic reactions
It’s not common, but it’s possible to have an allergic reaction to a flu shot. Signs and symptoms include:
Trouble breathing
Wheezing or a hoarse voice
Swelling of the face or neck
Hives
Feeling very weak
Extreme dizziness
Rapid heart rate
You’ll likely be asked to wait around after your vaccine to watch for any signs of an allergic reaction. But if symptoms appear after you’ve left, call 911 or seek emergency medical attention.
Good to know: If you have an egg allergy, talk to a healthcare professional before you receive a flu shot. Flu vaccines are likely safe even if you’re allergic to eggs. But there are egg-free options if your allergy is severe. Your pharmacist or prescriber can help determine which vaccine is best for you.
7. Febrile seizures in children
Another rare flu shot side effect is the possibility of febrile seizures in infants and children. These are seizures caused by a fever, so it's not a side effect that’s specific to the flu shot itself. And there’s only a small increased risk of febrile seizures if your child gets the flu shot at the same time as the pneumonia or diphtheria, tetanus, and acellular pertussis (DTaP) vaccine. There isn’t an increased risk of febrile seizures if the flu shot is given by itself.
Febrile seizures can happen any time a child has a fever. They may seem scary, but in most cases they’re harmless and don’t cause long-term problems. If you’re concerned about the risk of febrile seizures, talk to your pediatrician about separating your child’s flu shot from other vaccinations.
8. Guillain-Barré syndrome
One complication that’s a rare flu shot side effect is Guillain-Barré syndrome (GBS). GBS is a condition that can cause muscle weakness or paralysis. It happens when your immune system attacks and damages the nerves.
GBS is usually temporary, lasting a few weeks. But long-term nerve problems are also possible. GBS is considered a very rare side effect — it happens in about 1 to 2 people out of every 1 million people that receive the flu shot. And studies suggest that getting the flu may be more likely to cause GBS than the flu vaccine.
Talk to a healthcare professional about any concerns you have about GBS. They can look at your medical history to help determine if you’re at a greater risk for this side effect.
Frequently asked questions
It’s possible. A high-dose flu vaccine is recommended for those age 65 and over. This “senior flu shot” contains a higher dose to help activate the immune system of older adults. But this also makes them more likely to cause some side effects, such as injection-site reactions and headache. Talk to your pharmacist or prescriber about the best flu vaccine option if you’re over age 65.
The effectiveness of flu vaccines is different every year. Most years, the flu vaccine is about 40% to 60% effective. Keep in mind that it's best to get your flu shot before the end of October. It takes about 2 weeks for immunity to develop after the vaccine. So if you wait until the flu is active in your area to get vaccinated, it may not work as well for you (although it’s almost never too late to get your shot).
Yes, the flu shot is considered safe for most people, including infants and children as well as during pregnancy. We have more than 50 years of evidence backing up the safety of flu shots, and they remain the best way to protect yourself from the flu. The possible complications of a flu infection are far riskier than the side effects most people experience from the flu shot.
The bottom line
Getting a yearly flu shot is the best way to protect yourself from the flu. Flu vaccines are considered safe for most people. But the flu shot can sometimes cause side effects. It’s common to experience pain, swelling, or redness in the area where the flu shot is injected. Muscle pain, headaches, and general feelings of discomfort are also possible. But the flu shot can’t give you the flu. Most flu shot side effects are mild and should go away within a day or two.
Less common flu shot side effects and risks include fainting and allergic reactions. In very rare cases, Guillain-Barré syndrome can develop after a flu shot. It’s also possible for children to experience febrile seizures if the flu shot is given along with other vaccines. But these side effects don’t happen often. If you experience anything severe or excessive after getting a flu shot, reach out to a healthcare professional.
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References
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Centers for Disease Control and Prevention. (2024). Guillain-Barré syndrome (GBS) and vaccines.
Centers for Disease Control and Prevention. (2024). Key facts about seasonal flu vaccine.
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MedImmune, LLC. (2024). Flumist- influenza vaccine live intranasal spray [package insert]. DailyMed.
Musana, K. A., et al. (2004). Practical considerations to influenza vaccination.
Trombetta, C. M., et al. (2018). Influenza vaccines: Evaluation of the safety profile. Human Vaccines and Immunotherapeutics.
Usach, I., et al. (2019). Subcutaneous injection of drugs: Literature review of factors influencing pain sensation at the injection site. Advances in Therapy.
Wolicki, J., et al. (2024). Chapter 6: Vaccine administration. Centers for Disease Control and Prevention.
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