Can the Flu Shot Make You Sick? Facts and Safety Information

Influenza (or the flu) is a common respiratory illness caused by influenza viruses. And anyone who has had the flu knows it can make you feel pretty sick. But it can also cause more serious illness, hospitalization, and even death. In the U.S., roughly 5,000 to 50,000 people die every year from the flu. The flu shot is the best protection we have against the effects of the flu virus — and it’s safe.

The flu shot has been around for decades, and there’s plenty of research to support how safe and effective it is. But it’s understandable to have questions and concerns. Let’s take a closer look at the research so you can make the best choice for you and your community.  

Can you get sick from the flu shot?

Some people feel a bit under the weather after getting the flu shot. This isn’t because you’ve actually gotten sick with a virus though. When you get the flu shot, your body responds by mounting an immune response. During this process, your body works in overdrive to pump out antibodies that will protect you if you get exposed to the flu later on. This can make you feel mildly ill, but this feeling usually goes away within a day or so.

There are rare side effects that can make you sick in other ways. But the chance of a severe reaction from the flu shot is about 1 in 1 million. 

Is the flu shot safe?

The flu shot is a safe and effective way to protect yourself from the dangers of influenza. The flu shot can keep you from getting sick, and it even protects you if you do still end up getting the flu. 

There are a lot of misconceptions about the safety of the flu shot. The flu shot doesn’t cause:

• The flu

• Other respiratory infections

• Autism

• Bell’s palsy

Many organizations around the world monitor vaccine safety, like the Global Vaccine Safety Program of the World Health Organization (WHO). In the U.S., the CDC and the FDA both keep a close watch on vaccines. If a problem is found, they can quickly inform healthcare officials and the public. 

The CDC has three systems to monitor vaccine safety:

• Vaccine Adverse Event Reporting System (VAERS) is a national program that tracks side effects or other problems with vaccines.

• Vaccine Safety Datalink (VSD) is a joint program between the CDC and nine other healthcare organizations to track the safety of vaccines. 

• Clinical Immunization Safety Assessment (CISA) Project evaluates vaccine safety and does high-quality research with major medical centers.

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What side effects can flu vaccines cause?

As with any medical treatment, there are some risks to getting a flu shot. But the risk of health problems from a flu shot is very low. There are three main side effects you should know about.

Nonallergic reactions to the flu shot

Many people have only mild side effects from the flu shot, like local irritation or flu-like symptoms. These symptoms usually go away in 1 to 2 days and can include:

• Arm soreness from the shot (most common)

• Itching

• Fatigue 

• Cough

• Low fever

• Body aches

• Headaches

Mild reactions are a normal response to the antibodies your body makes due to the vaccine. Antibodies are the proteins that help your immune system prevent or fight infection the next time you come in contact with the flu.

Some people can also experience a brief fainting spell after getting a flu shot. This is especially common in adolescents. And in very rare cases, people can experience ongoing pain or stiffness at the injection site. 

Allergic reactions to the flu shot

It’s also possible that you could have an allergic reaction to the flu vaccine. This is usually caused by an allergic reaction to something else in the vaccine rather than the influenza virus fragments.

Allergic reactions to the flu shot can range from mild to severe. Mild reactions are not life-threatening. They can include symptoms like: 

• Hives

• Runny nose or cough

• Vomiting or diarrhea

A severe reaction — anaphylaxis — is serious and can be life-threatening. Symptoms of anaphylaxis include:

• Swelling of the face, lips, tongue, or throat

• Trouble breathing

• Dangerously low blood pressure

These reactions are rare. The chance of having an allergic reaction is about 1 in 1 million.  

Guillain-Barré syndrome

The flu vaccine has also been connected to Guillain-Barré syndrome (GBS). GBS is a serious autoimmune condition that causes temporary paralysis. It usually starts in the legs and can slowly work its way up the body. Even though these symptoms get better, this medical emergency can be scary.  

The risk of getting GBS from the flu shot is extremely small — about 1 in 1 million. It’s also important to know that the flu virus itself actually causes GBS in 17 out of 1 million people. This means you’re more likely to get GBS from being infected with the flu than from the vaccine.

Does the flu shot give you the flu?

No, you can’t get the flu from the flu shot. The flu shot is made from dead or weakened virus fragments that can’t make you sick. Mild symptoms that sometimes develop don’t mean you’re getting the flu. 

Can you get a flu shot when sick?

If you’re feeling sick, you should talk with a healthcare professional about your symptoms before getting the flu shot. Most experts agree that it’s safe to get the flu shot if you have a minor illness (like a runny nose or cold). But you may need to hold off on getting the flu shot if you have a more serious illness.

Is the flu shot safe for babies and children?

Yes, the flu shot is also safe for children. The flu shot doesn’t make children sick, and it doesn’t cause autism. In over 1.25 million children, no connection was found between autism and vaccines. 

Having the flu is dangerous for children. That’s why all children over the age of 6 months should have a flu shot every year. It’s the best way to protect children from serious flu-related illness, hospitalization, and death. 

Is the flu shot safe for pregnant women?

The flu shot has been studied for decades in millions of pregnant women. It’s safe and effective. Experts recommend that pregnant women should have a flu shot. 

Getting the flu can be dangerous for both the mother and the growing baby. Pregnant women may have medical complications if they get the flu. And they’re more likely to be hospitalized or die from the flu. The flu can also cause pregnancy complications like:

• Miscarriage

• Preterm labor

• Premature birth

Having the flu during pregnancy may even increase the baby’s long-term risk for conditions like:

• Autism

• Bipolar disorder

• Depression 

The flu shot protects both the mother and the baby during pregnancy. It will also protect the baby for up to 6 months after birth. This is especially important because babies younger than 6 months are too young for the flu shot. 

Is the flu shot safe for people with chronic medical conditions?

Yes. In fact, it’s especially important for people with chronic medical conditions to have a flu shot. The flu can also be especially dangerous for people who have a high risk for flu complications. This includes:

• Children under the age of 5, but especially children younger than 2 years

• Adults 65 years old and up

• People with a body mass index (BMI) of 40 or more

• People who are immunocompromised, including people with cancer

• Native Americans and Alaska Natives

• People living in nursing homes and other long-term care facilities 

• People experiencing homelessness

• People with diabetes

The flu can also worsen certain health conditions, like heart failure, chronic obstructive pulmonary disease (COPD), and asthma. 

Can the flu shot cause Alzheimer’s dementia?

The flu shot doesn’t cause dementia. In fact, new research suggests that regular flu shots may protect you against developing Alzheimer’s disease. In a 2020 study, having at least one flu shot decreased cases of Alzheimer’s by 17%. Repeat flu shots decreased it by another 13%. 

Should you get a flu shot?

Every choice has pros and cons, including getting the flu vaccine. But, for most people, the flu shot is likely to do more good than harm. The risks are very low. Compared with the flu shot, having the flu is actually pretty risky. 

The CDC recommends that everyone over the age of 6 months get a flu vaccine every year. Here are the only exceptions:

• If you’re currently sick with a fever, you should wait to get a flu shot. This doesn’t mean you can’t get the flu shot eventually, but you may have to wait until your current symptoms have passed.

• If you have a history of Guillain-Barré syndrome, talk with a healthcare professional before getting the flu shot.

• If you have a history of a severe, life-threatening allergy to an ingredient in the flu vaccine, avoid that vaccine — with egg allergy being the exception. The CDC still recommends flu shots for people with egg allergy.

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Written by:

Katie E. Golden, MD

Katie E. Golden, MD, is a board-certified emergency medicine physician and a medical editor at GoodRx.

Edited by:

Karla Robinson, MD

Karla Robinson, MD, is a medical editor for GoodRx. She is a licensed, board-certified family physician with almost 20 years of experience in health through varied clinical, administrative, and educational roles.

Reviewed by:

Farzon A. Nahvi, MD

Dr. Nahvi is an emergency medicine physician and author of “Code Gray: Death, Life, and Uncertainty in the ER.” He works clinically at Concord Hospital in Concord, New Hampshire, and is a clinical assistant professor of emergency medicine at the Geisel School of Medicine at Dartmouth. Prior to this, he worked as an ER physician and clinical assistant professor of emergency medicine at the Mount Sinai Health System, NYU Langone Health, NYC Health + Hospitals/Bellevue, and the Manhattan VA. He is a graduate of Cornell University and NYU School of Medicine.

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