Flu Vaccine Side Effects: What to Expect and How to Manage

Flu vaccine side effects are generally mild, but may include pain, redness, or swelling at the injection site, fever, muscle aches, headache, or fatigue. Learn what to expect and how to manage them.

Getting the flu vaccine every year is a smart move. It helps keep both you and your family safe from the serious effects of the flu. Even though the flu shot is usually safe, you might feel a few mild effects afterward.1 Knowing what these effects are can make things easier. It also shows you why getting the vaccine is worth it, even with these possible side effects.

Most people only have mild reactions to the flu shot. This can include pain, redness, or swelling right where you got the shot. You might also feel a bit feverish, achy, or tired, or get a headache.2 It’s rare to have a very serious reaction. But, if you’ve had a bad reaction before, make sure to tell your doctor. Remember, the flu shot itself cannot give you the flu. It’s made with parts of the virus that are weakened or dead, so they can’t make you sick.2

In fact, millions of people in the US have safely had the flu vaccine for decades.2 A lot of research has shown that flu vaccines are safe. By learning about the possible side effects, you can feel more at ease about getting your shot each year.

Key Takeaways

  • Flu vaccine side effects are generally mild, such as pain, redness, or swelling at the injection site, fever, muscle aches, headache, or fatigue.
  • Severe reactions, while rare, can include life-threatening allergic reactions and Guillain-Barré Syndrome (GBS).
  • The flu vaccine cannot cause the flu, as it contains inactivated or weakened virus strains that cannot cause illness.
  • Hundreds of millions of Americans have safely received flu vaccines over the past 50 years, and extensive research supports their safety.
  • Understanding potential side effects and how to manage them can help build confidence in receiving the annual flu shot.

Understanding Flu Vaccine Side Effects

The common flu vaccine side effects are usually mild. They can include redness, swelling or soreness where you got the shot. Some people might get a headache, fever, feel sick to their stomach, or have muscle pain.3 These side effects often go away in a few days.3

Common Adverse Reactions

Most side effects from the flu shot aren’t serious. But, in a few cases, severe reactions can happen. These include life-threatening allergic reactions and Guillain-Barré Syndrome (GBS), which can lead to weakness or paralysis.2 The chance of getting GBS from the flu shot is low. The flu itself is more likely to cause severe health problems.1

Rare but Serious Side Effects

Very severe reactions to the flu shot are uncommon. Guillain-Barré syndrome linked to the flu vaccine occurs in generally no more than 1 or 2 cases per million vaccinated,1. Severe allergic reactions are very rare after flu shots.1 Still, those with severe allergic reactions or a history of GBS should talk to their doctor.3

Pain, Redness, and Swelling at the Injection Site

A common reaction to the flu shot is some discomfort at the injection site. This includes soreness, redness, warmth, and a bit of swelling.4 These reactions usually go away in about two days. To make it less bothersome, you can take ibuprofen before the shot.4 Also, putting something cool on the spot can help.

Managing Injection Site Reactions

Flu shot injection site reactions can be managed. People can do things to help reduce flu vaccine injection site pain and cut down on flu shot redness and swelling. Take ibuprofen before the shot to lessen discomfort.4 And, use a cool compress on the spot for relief.4

flu shot injection site reactions

Headache and Body Aches

Headaches and body aches can happen after a flu shot. They usually start right after the shot and go away in two days. You can use over-the-counter pain meds to feel better. But, some think these meds might change how well the vaccine works.5

Flu vaccine headache and muscle aches after flu shot are common but not severe. Most people get through it with no more than a bit of temporary pain that fades in a few days.2 Over 50 years, millions of Americans have safely gotten their flu shots. The protection the vaccine offers is much more than the small risks of these side effects.2

Fever and Fatigue

If you get a fever after the flu shot, it’s usually not too high.6 It could feel mild and go away within a few days. But if the fever stays high or doesn’t go away, get medical help.6 Sometimes, feeling very tired can come with the shot. This goes away in a day or two.6 But, if the fever comes with worrying signs, contacting a doctor is wise.

When to Seek Medical Attention

It’s common to have a slight fever and feel tired after the flu shot.6 But, if the fever gets high or doesn’t stop, you should see a doctor.6 This could be a sign of a more serious issue. And if other symptoms appear with the fever, get help right away.1 Also, if you feel like you can’t breathe or have serious swelling or dizziness, go to the hospital at once.

Nausea and Vomiting

After getting the flu vaccine, some people might feel nauseous or throw up7. These side effects are not that common and usually go away quickly.7 If you feel very sick for a long time, it’s best to talk to a doctor. This could be a sign of a more serious problem.

In 2019, researchers looked at kids who had gotten a flu shot. They found that only a few of them, about 5 out of 210, had stomach pain7. Diarrhea was also rare after the shot, happening to about the same number of kids.7 Elderly people in another study also had some stomach issues, but these were very uncommon. Side effects in this group included various conditions like pancreatitis.7

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Extremely bad allergic reactions to the flu shot are not usual, but they can happen. This occurs if someone is allergic to things in the vaccine, like gelatin or egg.7 A condition called Guillain-Barré syndrome is a risk, but it’s very rare. It happens to 1 or 2 in 1 million people who get the vaccine. This is much less likely than getting very sick from the flu itself.7 The CDC says everyone 6 months and older should get the flu shot. This is especially true for kids, older adults, pregnant women, and those with certain health problems.7

Dizziness and Fainting

Some people feel dizzy or may faint after getting a flu shot. This happens because the body reacts to the shot.8 These reactions are not usually serious. Patients who faint should be watched by medical staff until they wake up.8

Precautions for Fainting Episodes

To avoid fainting, it’s best to sit or lie down after the flu shot. Eating a small snack before or after the shot can help too.8 Giving patients a drink, snack, or reassuring them can also prevent fainting.8

It’s important to stay where the shot was given for 15 minutes after. This is to make sure you don’t hurt yourself if you faint.8 If you feel dizzy or faint, tell the person who gave you the vaccine right away.

Flu Vaccine Side Effects

The flu shot may cause mild issues, like a sore arm or a low-grade fever, these often clear up within days.1 Rarely, but very importantly, some can get very ill from the vaccine. This includes severe allergic reactions or a nerve condition called Guillain-Barré Syndrome.12 For most, the shot is safe. Its good far outweighs the rare risks.

For example, the flu vaccine in 2019-2020 kept around 7 million from getting really sick with the flu.1 Those who were vaccinated and still ended up in the hospital were better off than the unvaccinated, with lower ICU stays and deaths.1 In the end, those who got the shot spent less time in the hospital.1

In the seasons from 2010 to 2015, the shot reduced how often older adults had to go to the hospital because of the flu.1 Kids got a lot of protection too, needing less intensive care or avoiding dangerous flu altogether.1 A flu shot during pregnancy halves the chance of getting very sick from the flu. It also makes flu-related respiratory problems much less likely for mom and baby.1

In another instance, from 2012 to 2015, the shot made a big difference for adults. It cut down on ICU admissions by 82%.1 Severe allergic reactions happen, but they’re rare and show up soon after the shot. 1 The risk of Guillain-Barré from the shot is very small, about 1 or 2 out of a million.12

Over the last 50 years, hundreds of millions of Americans have safely had flu shots.2 Now, it’s recommended for everyone 6 months and older every year.2 The chance of getting Guillain-Barré after a shot is extremely low.2 Allergic reactions can be serious but are very uncommon. They usually happen soon after the shot.2 If the shot does cause a severe problem, it should be reported.2 Anyone who might have a life-threatening reaction to the shot should avoid it.2 Yet, pregnant women should still get the shot. It helps to keep them and their baby safe.2 The CDC and FDA carefully watch over the flu shot’s safety. They check reports from VAERS and VSD.2

Allergic Reactions and Egg Allergy Considerations

Severe allergic reactions to the flu vaccine are very rare. Yet, they can cause breathing issues, hoarseness, swelling, hives, and dizziness.9 These symptoms usually show up within minutes to a few hours after the shot.9 If someone has had a bad reaction to the flu vaccine before because of egg protein or other things in it, they should check with their doctor before getting it again.9

Signs of Severe Allergic Reaction

If someone has trouble breathing, talking, or starts swelling, gets hives, or is dizzy after the flu vaccine, they need to see a doctor right away.

Egg Allergy and Flu Vaccination

Ongoing research by the CDC shows that most people with egg allergies can safely get any flu vaccine.9 It’s unlikely for these people to have bad reactions to flu shots or the nasal spray.9 Anyone over 6 months old with an egg allergy should get a flu shot every year.9 This is because only a tiny bit of egg protein is found in these vaccines.9

Few children or adults with egg allergies should worry about getting these vaccines. The tiny amount of egg protein left in the vaccine won’t cause harm.10 A large 2012 study found no severe cases after giving the flu shot to thousands with egg allergies.10 It’s very rare for anyone to have a bad reaction to these flu vaccines, about 1.35 cases per million.10

Guillain-Barré Syndrome and Flu Vaccination

In rare cases, the flu vaccine can be linked with Guillain-Barré Syndrome (GBS).11 GBS is a rare but serious condition. It can lead to muscle weakness and even paralysis. Yet, the chance of getting GBS from the flu shot is quite low. This risk is much lower than the risks linked with catching the flu without the shot.12

About 3,000 to 6,000 people in the U.S. get GBS each year. Mostly, symptoms show up days or weeks after a cold or stomach bug.12 In the U.S., 80 to 160 new cases of GBS are recorded each week, no matter if flu shots were given or not.12 Older adults, especially those over 50, face a higher risk of developing GBS.12

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After certain flu shots, like the 2009 H1N1 vaccine, studies found a small higher risk of GBS.11 Still, the general risk of GBS from flu shots is very low. To be exact, it’s about one to two more cases per million shots given.12

People who ever had GBS should talk to their doctor about the flu shot. While the GBS risk is low, they need to think about the shot’s possible side effects. It’s a balance between those and the benefits of avoiding the flu.11

Influenza Vaccine Safety Monitoring

The Centers for Disease Control and Prevention (CDC) and the Food and Drug Administration (FDA) watch closely over flu vaccine safety.2 They have a strong safety history spanning 50 years, given to hundreds of millions in the U.S.2 To keep flu shots safe, they rely on the Vaccine Adverse Event Reporting System (VAERS) and the Vaccine Safety Datalink (VSD).

Vaccine Adverse Event Reporting System (VAERS)

Managed by both the CDC and FDA, the Vaccine Adverse Event Reporting System (VAERS) is critical.2 It lets anyone report issues after getting a flu shot. This includes healthcare workers, the makers of vaccines, and the public.2 Info from VAERS helps catch any possible safety problems with flu vaccines.

Vaccine Safety Datalink (VSD)

The CDC and FDA also use the Vaccine Safety Datalink (VSD) to keep an eye on flu vaccine safety.2 This system constantly checks and searches data to uncover any safety issues early.13 For example, from 2013 to 2015, a thorough check happened as reported by Li R et al., 2016.13

With these systems in place, the CDC and FDA can fast-track any safety worries about flu vaccines. This ensures they remain a safe and effective solution for everyone to use.

Preventing Flu Vaccine Side Effects

To lessen flu shot side effects, drink a lot of water and rest well. This helps your body deal with any soreness, fever, or tiredness.2 You can also take over-the-counter pain relievers like acetaminophen or ibuprofen. They cut down on fever, headaches, and body pains. But, they might slightly lower how your immune system reacts to the vaccine.1

Hydration and Rest

Drinking enough water and getting plenty of sleep are vital for handling flu vaccine side effects. They help your body cope with minor issues like achiness, high temperature, or feeling worn out.1

Over-the-Counter Medications

Medicines you can buy without a prescription, such as acetaminophen or ibuprofen, can ease flu shot side effects. They help with headaches, sore muscles, and a fever. But, using them might slightly reduce the vaccination’s immune response.1 Before using these meds, think about their pros and cons.

When to Seek Medical Attention for Side Effects

Most flu vaccine side effects are mild and go away by themselves in a few days.2 If you get a high fever or have trouble breathing, it’s time to see a doctor. The same goes for feeling dizzy, swelling, or muscle weakness.2 If the side effects are bad and don’t go away, make sure to talk to a healthcare provider.

Over the last 50 years, millions have gotten the flu shot safely.2 Though side effects are usually mild and don’t last long,2 you should know the signs of a serious reaction.2 Very serious allergic reactions are rare, but they could happen soon after the vaccine.2 The risk of getting Guillain-Barré syndrome (GBS) is extremely low, at less than 1 or 2 people per million.2

If you develop a high fever, find it hard to breathe, or have lasting symptoms, call your doctor.2 They will check on you and offer the right care or advice.2 Quick action on any severe or worrying side effects is key. It helps keep you safe and healthy.2

Weighing the Benefits and Risks

Flu vaccines lower the flu risk by 40-60% when the viruses in the vaccine match those spreading.14 They also make the flu less severe, cutting down on hospital stays and saving lives.14 Though they might have some mild side effects, the protection they offer is more valuable, especially for the elderly, pregnant women, and those with ongoing health issues.

Flu Vaccine Efficacy

In the U.S., flu vaccines saved more than 40,000 lives from 2005 to 2014.14 In one season, 2011–2012, their effectiveness reached 71.4%.14 But, yearly, not all shots perfectly ward off the flu, with only 40–60% success.15 Yet, when matched to the right flu strains, they can cut flu risk by 40-60%.14

High-Risk Groups

Kids under 5, especially under 2, face more significant flu risks.14 For those 65 and up, a special high-dose vaccine is available for better protection.14 In kids aged 5-12, flu shots notably reduce the risk of flu-related deaths.15 Pregnant women benefit greatly too, with flu shots halving the risk of respiratory infections and dropping hospitalization chances by 40%.15


The flu vaccine is very safe and most people have no trouble with it.15 It might cause soreness, redness, or muscle aches where it was given. These are the most common side effects.15 Serious side effects are very rare but can happen. These can include serious allergies and a rare condition called Guillain-Barré Syndrome.15

Overall, the good things about getting a flu shot are better than the bad.15,16,17 This includes getting sick less, going to the hospital less, and not dying from the flu.15,16,17 Getting a flu shot each year is the best way to stay safe from the flu and its bad effects.15,16,17

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Flu shots lower the chance of getting sick with the flu by 40-60% during good seasons.16,17 They also make the sickness less bad, help people avoid hospital, and keep them from dying.16,17 Sometimes, flu shots can make people have mild side effects. Even so, the protection they offer is more important, especially for people at high risk. This includes older people, pregnant women, and those with health problems.16,17

When you get a flu shot every year, you are doing your part. It helps keep you safe and everyone around you.15,16,17 The flu shot is proven to be both safe and effective. It cuts down on how many people get sick, go to the hospital, and die from the flu each year.15,16,17


What are the most common side effects of the flu vaccine?

The most common side effects are at the injection site. You might feel pain, see redness, or notice swelling. Flu-like symptoms include fever, muscle aches, headache, and feeling tired. These side effects are usually mild and last only a few days.

What are the rare but serious side effects of the flu vaccine?

Rare but dangerous side effects can happen. These include severe allergic reactions and Guillain-Barré Syndrome (GBS). GBS is a condition that affects the nervous system. It can lead to muscle weakness and sometimes paralysis. But remember, the risk of GBS from the flu shot is very small compared to the risk from the flu itself.

How can I manage the pain, redness, and swelling at the injection site?

If you’re feeling discomfort at the injection site, there’s something you can do. Take over-the-counter pain relievers like ibuprofen. Applying a cold compress can also help. These steps can help and the discomfort will likely last for less than two days.

What can I do for headaches and body aches after getting the flu shot?

Headaches and body aches might affect you after the shot. You can use over-the-counter pain relievers to feel better. However, some debate whether these medicines can affect how the vaccine works.

When should I seek medical attention for a fever or fatigue after the flu shot?

A low-grade fever is a typical side effect and usually disappears in a day or two. But, if your fever is high or it lingers, seek medical help. This could be a sign of something more serious. Also, if the fever comes with other worrying symptoms, contact a doctor or nurse right away.

What should I do if I experience nausea or vomiting after the flu vaccine?

Feeling sick to your stomach or throwing up are less common effects of the flu vaccine. These usually go away after a day or two. However, if it’s bad or lasts a long time, see your healthcare provider. It might be a more serious issue.

What should I do if I feel dizzy or faint after getting the flu shot?

Feeling dizzy or even fainting are possible right after the flu shot. It’s due to how your body reacts. It’s recommended to sit or lay down for a bit after your shot. Eating something before or after can also help. If you do faint or feel dizzy, let someone know right away.

What are the signs of a severe allergic reaction to the flu vaccine?

Severe allergic reactions happen very rarely but they are serious. Signs include trouble breathing, hoarseness, swelling, hives, and dizziness. These issues usually show up soon after the vaccine is given. If you’ve had a bad reaction to the flu vaccine before, or if you’re allergic to its ingredients, talk to your healthcare provider first.

Is there a link between the flu vaccine and Guillain-Barré Syndrome?

There is an extremely rare connection between the flu shot and Guillain-Barré Syndrome (GBS). GBS can cause muscle weakness and even paralysis. Remember, GBS from the flu shot is very uncommon, much less so than severe flu complications. If you’ve had GBS before, think about the flu shot risks with your healthcare provider.

How are flu vaccine side effects monitored and reported?

The CDC and FDA keep a careful eye on flu vaccine safety. They use two main ways. The Vaccine Adverse Event Reporting System (VAERS) is for people to report issues they think are due to the vaccine. The Vaccine Safety Datalink (VSD) also helps by checking vaccine safety regularly.

What can I do to prevent or alleviate mild side effects from the flu vaccine?

To minimize mild side effects, stay hydrated and get plenty of rest. Over-the-counter pain relievers like acetaminophen or ibuprofen can help. But keep in mind, these drugs might slightly affect how your body responds to the vaccine.

When should I seek medical attention for flu vaccine side effects?

It’s important to get help if you have a high fever or show severe allergic reaction signs. These include trouble breathing, swelling, or dizziness. Symptoms of Guillain-Barré Syndrome, like muscle weakness or paralysis, also need immediate medical attention. If other side effects are really bad or don’t get better, contacting a healthcare provider is advised.

Source Links

  1. https://www.cdc.gov/flu/prevent/flushot.htm
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  3. https://health.baltimorecity.gov/flu/frequently-asked-questions-about-flu-vaccines
  4. https://www.healthline.com/health/flu-shot-side-effects
  5. https://www.goodrx.com/fluzone-quadrivalent/fluzone-quadrivalent-side-effects
  6. https://www.healthworks.com.au/flu-vaccine-side-effects/
  7. https://www.healthline.com/health/can-flu-shot-cause-stomach-upset
  8. https://www.cdc.gov/vaccinesafety/concerns/fainting.html
  9. https://www.cdc.gov/flu/prevent/egg-allergies.htm
  10. https://www.allergy.org.au/patients/food-allergy/egg-allergy-flu-vaccine
  11. https://www.cdc.gov/vaccinesafety/concerns/guillain-barre-syndrome.html
  12. https://www.cdc.gov/flu/prevent/guillainbarre.htm
  13. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5861790/
  14. https://www.medicalnewstoday.com/articles/312469
  15. https://www.medicalnewstoday.com/articles/flu-shots-pros-and-cons
  16. https://www.cdc.gov/flu/about/qa/vaccineeffect.htm
  17. https://www.cdc.gov/flu/vaccines-work/vaccineeffect.htm