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Key takeaways
The annual flu shot is recommended as the best protection against influenza, with the CDC highlighting its effectiveness in reducing illness risk by 40%-60% and its role in preventing virus transmission to vulnerable populations.
Common side effects of the flu vaccine are generally mild, including soreness, redness, and swelling at the injection site, along with potential low-grade fever, headache, and muscle aches, which indicate the body’s immune response.
Special high-dose flu vaccines are available for individuals 65 years and older, offering enhanced protection against the flu, albeit with a slightly higher risk of side effects such as muscle aches and headache.
Certain groups, including those with severe allergic reactions to previous vaccinations, children under six months, and individuals with Guillain-Barre syndrome history, are advised against receiving the flu shot, with healthcare provider consultation recommended for those with other specific health concerns.
An annual flu shot is the single best way to protect yourself and your family members against influenza viruses, according to the Centers For Disease Control and Prevention (CDC). But, during the 2020-201 flu season, only about 50% of adults in the United States received the flu vaccine and 59% of children. While that’s an increase of about 2% from the previous season, it still means that only half of the country chose to get the flu shot.
Reasons for vaccination hesitancy are numerous. Maybe you couldn’t find the time, or you felt like you were healthy enough to fight off the flu virus on your own. But when the flu vaccine is well-matched to circulating flu viruses, research shows it can reduce the risk of illness by 40%-60%. Also, getting the flu vaccine reduces the likelihood that you will pass the flu virus on to vulnerable family members or those who are not eligible to receive the vaccine.
Even in those who are otherwise healthy, getting sick with the flu puts you at risk for serious allergic reactions, but these are quite rare. For many, concern over flu shot side effects makes them avoid getting the injection, but is this fear warranted? Let’s take an in-depth look at the potential side effects of the influenza vaccination.
Flu shot side effects
Flu shot side effects generally fall into two categories: site reactions and systemic reactions.
Most side effects from the flu shot can occur soon after getting vaccinated and typically resolve within one to two days (and are local), says Ankur Patel, MD, a geriatrician and chief medical officer at Tabula Rasa HealthCare in Moorestown, New Jersey. Site reactions are a local response around the injection site that may include redness, swelling, soreness, discomfort, or pain. This type of reaction is the most common adverse effect of the flu shot. Dr. Patel adds that there are no long-term side effects associated with the flu shot.
Systemic reactions tend to be why otherwise healthy people think they’re getting sick from the flu, even when they aren’t. For example, you may experience a runny nose, headache, cough, fever, nausea, or muscle aches, and think you have the flu, Dr. Patel says. But these symptoms mean that your body is building immunity to the virus.
Vaccinations prepare and “teach” the immune system to be able to fight this year’s influenza virus, and mild symptoms are a sign that the immune system is learning and responding to the immunization,” Dr. Gendlina agrees.
For individuals over the age of 65 and children under the age of 5, getting vaccinated is even more important. That’s because young children and older adults are more likely to experience severe complications from the flu than younger individuals. There are two versions of the flu vaccine specially formulated for older people 65 years and up, the high-dose vaccine (Fluzone high-dose quadrivalent) and the adjuvanted vaccine (Fluad Quadrivalent).
The high-dose flu vaccine contains four times the antigens than the regular flu vaccine, Dr. Patel says. Because of this, it provides high-risk patients (individuals over 65) with a better immune response and enhanced protection from the flu. But side effects are more likely too, he says.
High-dose side effects—such as muscle aches, malaise, headache, and redness around the injection site—are the same as with the regular vaccine, but their frequency and severity may be greater with a high dose vaccine, Dr. Patel says. Even so, side effects are temporary, and will be minimal in most patients.
Who should not get the flu shot
According to Dr. Patel, the following groups of people should not get the flu shot:
- Patients who have had a severe allergic or life-threatening reaction to the flu vaccination in the past, such as difficulty breathing, severe wheezing, swelling around the eyes or lips, weakness, or a fast heartbeat.
- Patients who developed Guillain-Barre syndrome, a reversible reaction that causes complete or a partial loss of movement of muscles and/or a tingling sensation in the body, within six weeks of getting the flu shot.
- Children under six months of age.
- Pregnant women cannot get the nasal spray flu vaccine, but it is safe to receive an inactivated flu shot during pregnancy.
- Most people with allergies to eggs are eligible to receive flu vaccines but should talk to their vaccine provider because most flu shots contain egg products. Two vaccines (Flublok Quadrivalent and Flucelvax Quadrivalent) are licensed for use that are considered egg free.
Even if you’re not in one of these groups, Dr. Patel advises reaching out to your healthcare provider for guidance before receiving an influenza vaccine.
Common flu shot side effects
“The most common reaction to the vaccine is the body learning to fight off the flu,” says Bruce Hirsch, MD, an infectious disease specialist at Northwell Health in New Hyde Park, New York. The CDC reports that most flu shot reactions are mild and include:
- Soreness
- Redness
- Swelling at the injection site
- Low-grade fever
- Headache
- Nausea
- Muscle aches
- Fatigue
Some patients may experience loose stool, but diarrhea is not a common side effect of the flu vaccine, Dr. Patel says.
According to SingleCare’s 2021 flu shot survey, the majority of people who experience these reactions reported mild side effects.
Prevalence of flu shot side effects |
||||
|---|---|---|---|---|
| No reaction | Mild reaction | Moderate reaction | Severe reaction | |
| Injection site irritation | 56% | 20% | 20% | 4% |
| Muscle aches/weakness | 54% | 18% | 22% | 6% |
| Headache | 65% | 14% | 16% | 5% |
| Fever | 66% | 13% | 15% | 5% |
| Nausea | 72% | 11% | 13% | 4% |
While not enjoyable, these vaccine side effects show that your body’s immune system is responding to the vaccine. “Soreness is common at the site of the injection for a few days,” Dr. Hirsch says. “The injection goes into your shoulder muscle, which can cause soreness, but it’s also a sign of the body’s reaction to the shot as there is an immune response at the site of the jab.”
A common myth about the flu shot is that it can give you the flu. “It is impossible to get the flu from the flu shot,” says Dr. Hirsch. “There is no flu virus in the vaccine to cause the flu.” Vaccines are made with either inactivated (dead) virus or a piece of protein from the flu virus to guide the immune system to make antibodies against it. In other words, the shot and nasal spray vaccine are incapable of causing infection.
RELATED: Can you get the flu from the flu shot?
Rare side effects of flu shots
In addition to the common side effects listed above, there are a few rare side effects of the flu vaccine. According to the SingleCare survey, respondents experienced these more uncommon side effects:
Prevalence of uncommon flu shot side effects |
||||
|---|---|---|---|---|
| No reaction | Mild reaction | Moderate reaction | Severe reaction | |
| Fainting | 84% | 7% | 7% | 2% |
| Difficulty breathing | 83% | 7% | 8% | 2% |
| Allergic reaction | 82% | 8% | 7% | 3% |
| Shoulder injury related vaccine administration (SIRVA) | 85% | 6% | 7% | 2% |
| Guillain-Barre syndrome | 88% | 5% | 5% | 2% |
Guillain-Barre syndrome (GBS) is a neurological health condition that causes severe weakness—but again, it is a very rare side effect of the flu shot. “Some studies find 1 to 2 out of a million people get this complication after the flu shot,” Dr. Hirsch explains. “Other studies find no association. Guillain-Barre is more common after the flu than after the flu shot.”
In rare instances, serious side effects may occur that warrant medical attention from your healthcare provider. “Most people are asked to stay for observation after a vaccine, in case of syncope (temporary loss of consciousness) or dizziness, which typically happens within 20 minutes,” says pediatric pulmonologist Kunjana Mavunda, MD, of Kidz Medical Services of South Florida. “But that is usually a psychosomatic reaction because those are people who tend to be anxious about shots.
Signs of an allergic reaction to flu shots
What about flu shot allergies? If you’re able to eat scrambled eggs, you shouldn’t have a problem. But if you do have an egg allergy, it’s important to speak with your healthcare provider.
“Most flu vaccines are currently made using eggs,” Dr. Hirsch says. “There are microscopic amounts of the egg protein ovalbumin in most vaccines. Persons with severe egg allergic reactions (difficulty breathing, low blood pressure, requiring emergency care) should get the flu shot with egg-free vaccines such as Flublok Quadrivalent and Flucelvax Quadrivalent.”
The following may be signs of a severe allergic reaction:
- Difficulty breathing
- Hoarseness or wheezing
- Swelling of the lips or around the eyes
- Hives
- Paleness
- Weakness
- Rapid heart beat
- Dizziness
What should I do if I have a serious reaction to the flu vaccine?
If you are having a serious allergic reaction to the flu vaccine, Dr. Patel says it’s best to seek medical help by calling 911, get to the nearest hospital, or call your doctor right away.
How to treat flu shot side effects
To minimize flu shot side effects, Dr. Patel recommends the following:
- Apply ice or a cold compress to the injection site to help reduce pain and swelling if you experience soreness.
- Apply warm packs to muscle aches.
- Avoid activities that add tension to your arm, such as working out or lifting heavy objects.
- Try to get your flu shot on a Friday or Saturday, which will help you recover from any potential side effects over the weekend.
- Take a pain reliever like Tylenol (acetaminophen) or Motrin (ibuprofen) for soreness or discomfort.
“If you have a high fever greater than 101.5 within 24 to 72 hours after the vaccine or if the local reaction gets worse after 24 hours, then you should contact your physician,” Dr. Mavunda advises.