Can The Flu Vaccine Make You Sick?

With flu season in full swing, it’s time to schedule your next vaccine appointment. If you’ve never had a flu shot before, or are just in need of a refresher, you’re probably looking for some insight on what to expect afterward.

ICYDK, flu viruses typically spread in early fall and winter, peaking between December and February, according to the FDA. But because the virus mutates, every flu season is different, meaning the health impact varies widely from year to year. As a result, the flu vaccine is updated every year to protect against new flu virus strains that are expected to circulate and cause illnesses. That means you do, in fact, need a flu shot every year.

Still, it’s totally understandable to have concerns about the shot’s potential side effects. But the first thing to note is that the vaccine reduces the risk of life-threatening disease somewhere in the range of 40 to 60 percent, and as high as 75 percent among children, per the CDC.

There’s also the long-running myth that getting your flu shot will give you the flu. However, it is not possible to contract influenza from the vaccine, says Michael Hanak, MD, the associate chief medical officer for Population Health. “The vaccine is made from inactivated viral particles, which do not cause illness.”

While it won’t give you the virus, many people experience mild flu-like symptoms after vaccination, which is a sign that your body is producing antibodies and generating an immune response. And that’s a good thing!

Meet the experts: Michael Hanak, MD, is a board-certified family physician and associate professor in the department of family & preventive medicine at Rush Medical College.

Sindhu Aderson, MD, is the medical director of Northwestern Medicine Immediate Care.

Amesh A. Adalja, MD, is an infectious disease physician and a senior scholar at Johns Hopkins University for Health Security.

Soma Mandal, MD, is an internist at Summit Medical Group in Berkeley Heights, New Jersey.

It’s more important than ever to get vaccinated this year.

Influenza is responsible for thousands of hospitalizations and hundreds of deaths each year, and while the flu vaccine does not protect 100 percent of people from actually contracting the flu, much like the COVID vaccine, it can prevent severe illness.

And side effects are transient and typically last one to two days after vaccination, says Sindhu Aderson, MD, the medical director of Northwestern Medicine Immediate Care. People who are vaccinated and get sick anyway tend to experience less severe symptoms as well as decrease their risk of hospitalization. “This is why the flu shot is an incredibly important tool to keep ourselves and those around us safe,” says Dr. Aderson.

If you are thinking of getting a flu shot this year, plan accordingly. The vaccine can take 14 days to take full effect, according to Dr. Hanak, so take into account any holiday plans or upcoming travel.

The vaccine is not effective immediately, so people who were exposed to influenza or another virus shortly before or after getting their shot may still get sick, completely unrelated to their vaccination.

Another thing to note? Talk of the flu shot’s many side effects tend to be exaggerated. We repeat: The flu shot can’t actually give you the flu, and while there are some possible side effects, most are rare, says infectious disease expert Amesh A. Adalja, MD, a senior scholar at the Johns Hopkins Center for Health Security.

If you’re particularly wary of needles, you may prefer the nasal influenza spray (Flumist) over an injection, says Soma Mandal, MD, an internist at Summit Medical Group in Berkeley Heights, New Jersey. “Not everyone should get the nasal flu spray due to factors like age and underlying health conditions, though, so talk to your doctor to determine if it’s the best option for you,” she adds.

The flu shot is still worth it despite potential side effects.

Here are the flu shot side effects to be aware of this season, from common soreness and redness to rare effects like Guillain-Barre syndrome. After you’ve read through them, roll up your sleeve because flu season is coming. And the vaccine is still your best stay-healthy defense.

1. Shoulder Soreness

If you receive the flu shot as an intramuscular injection (a.k.a. in your arm, typically), odds are you may end up with some muscle soreness in your upper arm

That’s because the needle is injected directly into the muscle, causing microscopic damage to the cells, and is designed to cause an inflammatory immune system response. If the pain is very noticeable or decreases your mobility, Dr. Adalja recommends checking with your doctor.

What to do: If you are experiencing shoulder soreness, especially at the injection site, you can opt for an over-the-counter medication such as acetaminophen (Tylenol).

2. Redness Or Swelling

Anytime you pierce the skin and put something into the body, it can cause a topical reaction, says Dr. Adalja. This is just a sign that your immune system is activating.

But this redness and swelling where you get your shot is a common side effect that only typically lasts a few days. It’ll go away on its own, but if it’s really bugging you, you can take acetaminophen.

What to do: Try avoiding activities involving the shoulder immediately after your shot, and to take [medication] as needed, says Dr. Hanak. You may even want to schedule your flu vaccine before a weekend or a day off from the gym to avoid having to use your arm, which may be sore post-vaccination.

3. Body Aches

Any vaccine can cause body aches because of the way in which they activate the immune system, says Dr. Adalja.

If you’re feeling sore in places other than your arm, it’s usually nothing to worry about, though Dr. Adalja notes that the flu shot does take two weeks to become fully effective—so your body aches could be a sign of the flu, since viral strains are probably circulating around the time you get the vaccine.

What to do: Hydrating with plenty of water and taking acetaminophen is your best bet at relieving body aches.

4. An Allergic Reaction

While it’s extremely rare, it is possible to have an allergic reaction to the flu shot. Any medication or vaccination has the potential for adverse effects including severe life-threatening reactions, says Dr. Mandal.

In some cases, this can look like itching at the injection site, a full-body rash, or signs of anaphylactic shock, which would require immediate medical attention. In more severe cases, you may experience hives, wheezing, shortness of breath, fast heart rate and dizziness within a few hours of receiving the vaccine.

“There are lots of myths about egg allergies and the vaccine,” explains Dr. Adalja—because most flu shots and nasal sprays are manufactured using technology that involves small amounts of egg proteins, per the CDC. But in reality, you can likely get the shot even if you’re allergic to eggs, the CDC says.

BTW, if you’ve had an allergic reaction to the flu shot in the past, you are among those few groups of people who the CDC recommends skip the flu shot.

What to do: For a local reaction, Dr. Hanak recommends taking an allergy medication like Benadryl or using any anti-itch creams or lotions like a topical Benadryl cream to help with the discomfort. In severe situations, take allergy medication if it’s immediately available, and call 911 to go to the hospital. In some instances, you may need steroids or other treatments to help quell these flu shot side effects if they are severe.

5. Fever

You probably won’t get a fever because of the vaccine, but if you do, it should be low-grade (i.e. less than 101 degrees). If it’s higher than that, don’t blame your flu shot—you probably have an unrelated illness. “Remember that you’re getting the vaccine at the height of respiratory virus season,” says Dr. Adalja. “So you may have been incubating another virus [without knowing it].”

And once again (for the people in the back!): The flu shot cannot give you the flu. While some flu vaccines contain virus strains, they’re not live strains, so they can’t get you sick. Meanwhile some flu shots only contain a specific protein from the influenza virus, per the CDC.

What to do: Drink cold fluids, stay hydrated, and take acetaminophen until the fever subsides, says Dr. Hanak.

6. Dizziness Or Fainting

This is less a side effect of the vaccine itself and more a side effect of a needle phobia, says Dr. Adalja. If you think you might have a stress reaction or faint, give your health care provider a heads up so they can make sure you stay seated after the shot to prevent injury.

What to do: Dr. Hanak advises monitoring your blood pressure and reporting to your doctor. You should also do your best to stay hydrated.

7. Headache

An aching head is included in the CDC’s official list of potential side effects, but it’s nothing to panic over. “It is just part of the immune reaction to the vaccine,” says Dr. Adalja, adding that it usually goes away pretty quickly and can “easily” be treated with acetaminophen. FWIW: Some of the headaches could just be due to anxiety about getting a shot, Dr. Piedra says. “People could receive a placebo shot and get headaches as well,” he says.

What to do: Drink plenty of fluids and take some acetaminophen until your headache subsides.

8. Nausea

This is another one listed by the CDC that Dr. Piedra says is likely due to anxiety. “There are people that, when they get an injection of whatever type, can have some gastrointestinal manifestations afterward, including nausea,” he says. “It’s often attributed to anxiety.” It’s possible to have a little nausea as a larger part of your body’s response to the flu vaccine, Dr. Adalja says, but it doesn’t last long. “It will flee rapidly,” adds Dr. Piedra.

What to do: Consider OTC options like Dramamine, ginger supplements, or Pepto-Bismo to tame your stomach. You may want to make some dietary changes depending on what types of beverages and foods your stomach can handle.

9. Guillain-Barre Syndrome

Guillain-Barre syndrome (GBS) is an auto-immune disorder that’s triggered by a wide variety of things, from vaccines to viral infections.

GBS causes damage to the nervous system, resulting in symptoms like muscle weakness, numbness, difficulty walking or an odd gait, and even paralysis, says Dr. Adalja. While most people fully recover from the disorder, the recovery period can range from six months to three years, according to Mayo Clinic.

The connection between GBS and the flu vaccine has also been overhyped. “People should remember that influenza itself is much more likely to cause GBS than the vaccine,” adds Dr. Adalja.

And since no more than one or two cases per million people vaccinated will have this side effect, it’s better to take your (super small) chances with GBS than with one of the many common, severe complications that often come with the flu itself. Studies have shown that the likelihood of contracting GBS is actually higher after having influenza than after receiving the influenza vaccine, notes Dr. Hanak. “On average we see one to two cases per million vaccinations, but the evidence is not clear yet as to how strong a link exists.” For example, 13 million older adults showed no increase in GBS following flu vaccination, a recent study published in JAMA reported.

What to do: If you experience any of the symptoms of GBS, it’s best to check in with your doctor about next steps.

10. Fatigue

Another flu shot side effect is fatigue and a runny nose, notes Dr. Hanak. Just like other symptoms that stem from the body’s immune response these are “usually short-lived,” he says.

What to do: If the side effects are bothersome, drink plenty of fluids, rest, and use nasal decongestants for nasal symptoms.

Why do some people get side effects and others don’t?

It is estimated that up to 20 percent of people with influenza do not exhibit symptoms, which further shows everyone needs to get vaccinated, explains Dr. Hanak. “Similarly, varying levels of immune response occur with the flu vaccine, which can produce a wide variety of symptoms, including none at all,” he says.

Many factors can play a role, including age, medications taken regularly, other health conditions, and timing (i.e., receiving the shot when you have seasonal allergies or other ongoing illnesses).

The flu vaccine is designed to stimulate your immune system to build antibodies against the virus, and the thought here is that those people having side effects from the flu shot are those whose bodies are having a robust response to the vaccine, says Dr. Aderson. That said, not experiencing flu shot side effects does not mean that the vaccine didn’t work.

As with many things in life, everybody and every body will respond differently to the flu shot depending on many different factors.

Sabrina is an editorial assistant for Women’s Health. When she’s not writing, you can find her running, training in mixed martial arts, or reading.