Every year, people protect themselves from influenza, or the flu, by getting the flu vaccine. This vaccine, which typically comes as a shot or nasal spray, can reduce your chances of getting the flu by as much as .

Most side effects from the flu shot are typically mild. However, in rare cases, they can be severe. Before you get your flu shot, you may want to know what to expect. Read on to learn about common and rare side effects of the flu shot as well as how to reduce these effects.

A mercury-based preservative called thimerosal is used in some multidose vials of the flu vaccine. It’s used to prevent bacteria and other germs from growing. According to the , thimerosal use in vaccines is safe and causes few side effects. If you’re concerned about thimerosal, you can ask for a vaccine that doesn’t contain it. This lists currently available flu vaccines and whether they contain thimerosal.

The more common side effects of the flu shot are mild. They’re the same in adults, children, and babies.

Reaction at the injection site

The most common side effect of the flu shot is a reaction at the injection site, which is typically on the upper arm. After the shot is administered, you may have soreness, redness, warmth, and in some cases, slight swelling. These effects usually last less than two days. To help reduce discomfort, try taking some ibuprofen before getting your shot.

Headache and other aches and pains

After your shot, you might have headaches or some achiness and pain in the muscles throughout your body. This also usually happens on the first day and goes away within two days. Taking pain relievers can help ease your discomfort.

It’s controversial whether it’s safe to take acetaminophen or ibuprofen to treat these vaccine side effects. Some research suggests that these medicines might change or decrease how your body responds to the vaccine.

Other research is mixed and it’s still unclear whether these medications should be avoided. found that taking acetaminophen or ibuprofen didn’t reduce the body’s response to the flu vaccine.

Dizziness or fainting

Some people experience dizziness or fainting with the flu shot. These effects shouldn’t last longer than a day or two. If you tend to get dizzy or faint when getting a shot, be sure to tell the healthcare provider before they give you the flu shot. You can also try sitting for a while after you receive the shot and having a snack before or after the shot.

Fever

A fever of 101°F (38°C) or less is a common side effect of the shot. A slight fever is considered a mild side effect, and it should go away within a day or two.

If the fever bothers you, you can consider taking ibuprofen or acetaminophen. As we noted above, some concern has been raised that both acetaminophen and nonsteroidal anti-inflammatory drugs, including ibuprofen or naproxen, could diminish the body’s response to vaccines, but research isn’t conclusive at this time.

Q:

Does the nasal spray flu vaccine cause different side effects than the flu shot?

A:

Like the flu shot, the flu nasal spray — also called the live attenuated influenza vaccine (LAIV) — may cause headache, slight fever, dizziness, and fainting.

However, the nasal spray can also cause other side effects that the shot doesn’t, including tiredness, loss of appetite, runny nose, and sore throat.

Please note, the nasal spray isn’t available every year. Check the CDC website for more information.

Healthline Medical TeamAnswers represent the opinions of our medical experts. All content is strictly informational and should not be considered medical advice.

Serious side effects are rare with the flu shot, but they can include:

High fever

A fever greater than 101°F (38°C) isn’t common. If you’re concerned about a high fever, call your doctor.

Severe allergic reactions

Rarely, the flu vaccine can cause a severe allergic reaction. Severe allergic reactions usually happen within a few hours of receiving the vaccine. Symptoms include:

  • hives
  • swelling
  • trouble breathing
  • fast heart rate
  • dizziness
  • weakness

If you have any of these symptoms, call your doctor right away. If they’re severe, call 911 or go to the nearest emergency room.

Guillain-Barré syndrome (GBS)

In very rare cases, some people who have received the flu vaccine have experienced Guillain-Barré syndrome (GBS), a neurologic condition that causes weakness and paralysis throughout your body. However, it’s not clear if the flu vaccine is the actual cause of GBS in these cases.

GBS is more likely to occur in people who’ve had GBS in the past, so be sure to tell your doctor if you have a history of this condition. That said, having GBS in the past doesn’t always mean you can’t receive the flu vaccine. Talk to your doctor to find out if the flu vaccine is safe for you.

Call your doctor right away if you have symptoms of GBS after receiving the flu shot.

The flu shot is typically recommended for everyone ages 6 months or older. Anyone at risk of serious complications from the flu should also receive the flu shot. These include pregnant women, people older than 65 years, and people with chronic diseases as well as their caregivers.

The shot isn’t recommended for people who:

  • have had an allergic reaction to the flu shot in the past
  • have a severe allergy to eggs
  • are currently sick with a moderate-to-severe fever

The flu shot is a safe, effective treatment with few side effects. Still, if you’re concerned, you can talk to your doctor or pharmacist. They can help you decide if a flu shot is right for you. Questions you may ask include:

  • Is getting a flu shot a good idea for me?
  • Which flu vaccine is best for me?
  • Am I at risk of serious complications from the flu?
  • Am I at high risk of side effects from the flu shot?

Q:

Can I get a flu shot if I’m allergic to eggs?

A:

Most flu vaccines are made using eggs, so they could cause a reaction in people with an egg allergy. In the past, the CDC advised many people with an egg allergy to avoid getting the flu vaccine. But now, the CDC says that most people with egg allergies can safely get the flu vaccine.

Whether you can receive the flu vaccine or not depends on how severe your egg allergy is. If you’ve only had hives as a reaction to eggs, you can get any flu vaccine that’s otherwise safe for you. If you’ve had other symptoms from eggs, such as swelling or lightheadedness, you should only get the flu vaccine from a healthcare provider who’s trained to handle an allergic response. But if you’ve ever had a severe reaction to eggs, the recommendation is that you should still not get the flu vaccine.

If you have an egg allergy, talk to your doctor about getting a form of the vaccine that’s safe for you.

Healthline Medical TeamAnswers represent the opinions of our medical experts. All content is strictly informational and should not be considered medical advice.