Can you get sick from the flu shot?

Medically reviewed by Dr. Betsy Koickel, MD on January 22nd 2026.

With flu season upon us, the flu shot is your best available protection against the flu. Even though the dominant flu strains are constantly changing every year, getting the flu shot still lessens the risk of severe illness from any strain of the flu.

Getting the flu vaccine not only protects you, but it also protects those around you and your loved ones. If you are pregnant or have a baby, getting the flu shot can help keep you healthy and reduce the risk of spreading the flu to others.

Because of this, the Centers for Disease Control and Prevention (CDC) recommends an annual flu shot for everyone six months of age and older to reduce the risk of illness and prevent the spread to others.

If you are concerned about the potential side effects of the flu shot, speak to a trusted medical professional for personalized guidance.

Understanding the flu shot

Flu vaccines contain inactivated (killed) viruses or recombinant proteins that cannot cause the flu. Once you take the flu shot, the body starts to develop antibodies against the virus within about two weeks. This is why it is recommended that you take the flu vaccine a bit before or right at the start of flu season, so your body has time to develop the immune response before you are exposed to the virus.

You need a flu vaccine annually because the flu virus mutates and changes over time. As of the 2024-2025 flu season, all flu vaccines in the United States will be “trivalent,” meaning they will protect against three different flu strains. 

Why you can't get the flu from the flu shot

Despite what many might believe, you cannot get the flu from the flu shot because it does not contain an active virus. There is also no evidence that the flu vaccine increases your risk of other respiratory illnesses. 

But after getting the vaccine, you could develop a mild vaccine reaction  for a few different reasons:

• Flu vaccine reactions: Some people do develop muscle aches or low-grade fever after a flu vaccine, but this does not mean you have the flu.
• Other illnesses: Many illnesses are circulating during the fall and winter, so if you do get a respiratory illness, it could be a different virus.
• Mismatched flu viruses: In some years, the circulating flu virus is a mismatch to the available flu vaccine, making it less effective. 
• Two-week window: It takes two weeks for the flu vaccine to take effect, so you could catch the flu before the immune response is complete. 

Overall, the flu vaccine offers protection from the flu with minimal negative side effects. This is why the CDC recommends them for almost everyone.

Flu shot reaction in adults

Flu shot side effects are possible but are generally mild. The most common side effects in adults include:

• Fever
• Headache
• Muscle aches
• Nausea
• Swelling/redness around the injection site

Some studies have found a potential small link between the flu vaccine and Guillain-Barré syndrome (GBS), with about 1-2 cases per 100,000. This is a rare disorder where the body’s immune system attacks the nerves of the body, leading to paralysis in some severe cases. 

The estimated risk is one to two cases of GBS per one million people vaccinated, and it is more likely to occur due to an infection like the flu rather than the vaccine itself.

Large CDC surveillance studies continue to find that seasonal flu vaccines are overwhelmingly safe, with the flu shot benefits of preventing severe illness far outweighing this extremely small potential risk of hospitalization or death.

Flu shot reaction in children

The reactions to flu shots in children are similar to those in adults. Most side effects appear within the first 24–48 hours and resolve on their own. 

The main difference is that children are more likely to develop a temporary flu shot fever as a side effect than adults. Other flu vaccine reactions in children may include: 

• Body aches
• Fatigue
• Headache
• Low-grade fever
• Nausea
• Soreness, redness, or discomfort at the injection site
  

In rare cases, if a child is allergic to one of the ingredients in the shot, they may have an allergic reaction to the flu shot. Parents should seek medical attention if a child develops difficulty breathing, widespread hives or a persistent high fever. 

In the case of a fever, Tylenol can be taken. While flu shot side effects are possible, the benefits of flu vaccine protection outweigh the potential risks of infection. Just like in adults, a child can’t get the flu from the flu vaccine. 

Overall, flu vaccines have an excellent safety profile in children, and the risk of flu-related complications is far greater than the risk of vaccine side effects. This is why the flu vaccine is recommended annually for all children six months and older.

Risks of not getting the flu shot

While there is a small risk of side effects from the flu shot, there are more significant risks associated with not getting it.

The CDC estimates that up to 20% of Americans will contract the influenza virus each year, and between 100,000-710,000 will be hospitalized due to flu-related complications. Not getting the flu shot poses a bigger risk to overall health.

In particular, not getting the flu vaccine increases the risk of more severe illness, hospitalizations and death in rare cases. This is especially true in those with compromised immune systems, such as pregnant women and the elderly.

Common flu vaccine myths

Despite what the research shows, a few common flu shot myths persist. Many wonder, “Can you get sick from the flu shot?” among other myths, such as:

• I’ll wait until I get the flu to get a shot.
• I’m healthy and don’t need one.
• I’ve gotten the flu shot before, so I don’t need another. 
• The flu shot doesn’t do much.
• The vaccine causes autism.
• The vaccine causes infertility.
• The vaccine can overload your immune system.
• The vaccine contains toxins.
• The vaccine gives you the flu.

Fortunately, none of these myths is backed by research. Most myths stem from misunderstandings about how the vaccine works.

If you have questions or concerns about the flu vaccine or a flu shot reaction, speak to a trusted medical professional who will discuss the facts and recommended vaccination scheduling with you.

Flu shot FAQs

Here are some frequently asked questions about the flu vaccine and flu shot safety:

Can the flu shot give me the flu?

No. Flu shots use inactivated virus or recombinant proteins, which cannot cause influenza.

What are the common side effects of the flu shot?

Mild symptoms like soreness, redness, low-grade fever, headache, fatigue or muscle aches are the most common.

How long do side effects last?

Flu shot side effects typically appear within 24 hours and resolve within 1–2 days.

Are there any serious side effects?

Serious reactions such as severe allergy or Guillain-Barré syndrome are extremely rare, occurring in about 1–2 cases per million doses.

Should I get the flu shot if I'm healthy?

Yes. Healthy adults still benefit from vaccination because it reduces the risk of illness, hospitalization and spreading influenza to others.

Visit urgent care for your flu shot

Flu season is upon us, and one of the best ways to protect yourself from serious illness is by getting the flu shot. To obtain your flu shot, find the center nearest you, walk in today, or save your spot online.

References: 

1. https://pmc.ncbi.nlm.nih.gov/articles/PMC9143275/
2. https://www.cdc.gov/flu/vaccines/keyfacts.html
3. https://www.mayoclinic.org/diseases-conditions/flu/in-depth/flu-shots/art-20048000
4. https://pmc.ncbi.nlm.nih.gov/articles/PMC9804417/
5. https://www.cdc.gov/vaccine-safety/vaccines/flu.html
6. https://www.cdc.gov/flu/hcp/infection-control/healthcare-settings.html