About the flu shot

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 60 percent.

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.

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 Centers for Disease Control and Prevention (CDC), 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 CDC table 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 given, 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 medications might change or decrease how your body responds to the vaccine. One study involving children found that taking acetaminophen or ibuprofen didn’t reduce the body’s response to the flu vaccine.

Other research is mixed. It’s still unclear whether these medications should be avoided.

Dizziness or fainting

You may 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 your healthcare provider before they give you the flu shot.

You can also try:

  • sitting for a while after you receive the shot
  • having a snack before or after the shot


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

If the fever bothers you, you can consider taking ibuprofen or acetaminophen.

As noted above, some concern has been raised about both acetaminophen and nonsteroidal anti-inflammatory drugs, including ibuprofen or naproxen. The concern is that these medications could diminish the body’s response to vaccines. However, research isn’t conclusive at this time.

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). GBS is 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. 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, which includes:

  • pregnant women
  • people ages 65 and older
  • people with chronic health conditions 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?