Flu Shot: Learn the Side Effects

Side effects from the influenza vaccine are generally mild and short-lived, typically resolving within a day or two. The most frequent complaint is tenderness or swelling where the shot was administered. Health professionals usually advise getting the vaccine annually unless you have specific allergies.

Each year, many people protect themselves against influenza — commonly called the flu — by receiving the flu vaccine. Available as an injection or a nasal spray, this vaccine can lower your likelihood of needing medical care for the flu by up to 60 percent.

Most reactions to the flu vaccine tend to be minor. In rare instances, they can be more serious. If you’re planning to get vaccinated, it can help to know what reactions are possible.

Some multidose flu vaccine vials contain a mercury-based preservative called thimerosal to prevent bacterial contamination. The Centers for Disease Control and Prevention (CDC) states that thimerosal in vaccines is considered safe and rarely causes adverse effects.

If you’re uneasy about thimerosal, you can request a formulation that doesn’t include it.

Most common flu vaccine reactions

The typical side effects from the flu vaccine are usually mild and affect adults and children similarly.

Injection site reaction

The most frequent reaction is at the injection location, normally the upper arm. After receiving the shot, you may notice soreness, warmth, or a small amount of swelling. These symptoms commonly subside within two days.

Headache and body aches

Headaches or muscle aches can occur after vaccination. These usually appear on the first day and disappear within 48 hours. Over-the-counter pain relievers can help reduce discomfort.

There’s debate about whether taking acetaminophen or ibuprofen to treat these post-vaccine symptoms is advisable.

Some studies indicate these medicines might alter or lessen the immune response to the vaccine.

Other findings are inconsistent, so it remains uncertain whether these drugs should be avoided.

Dizziness or fainting

Dizziness or fainting can happen with the flu vaccine but typically resolves within a day or two. If you faint or feel lightheaded when getting shots, inform the healthcare provider before vaccination.

To reduce risk, you can:

• remain seated for a few minutes after the injection
• eat a snack before or soon after receiving the vaccine

Q:

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

A:

Similar to the shot, the nasal spray — known as the live attenuated influenza vaccine (LAIV) — can cause headache, dizziness, fainting, and a slight fever. The nasal version may also produce symptoms not typical of the injection, such as fatigue, reduced appetite, a runny nose, and sore throat. Keep in mind the nasal spray isn’t offered every season; see the CDC for more details. For natural symptom relief options, you might also consider essential oils for flu.

Serious reactions to the flu vaccine

On rare occasions, the flu vaccine can trigger a severe allergic reaction. These serious allergic events usually occur within a few hours of vaccination. Signs may include:

• hives
• rapid heartbeat
• difficulty breathing
• dizziness
• generalized weakness

If you experience any of these symptoms, seek immediate medical assistance. For severe reactions, call 911 or go to the nearest emergency department.

Guillain-Barré syndrome (GBS)

Very rarely, some individuals have developed Guillain-Barré syndrome (GBS) after receiving the flu vaccine. GBS is a neurological disorder that can cause widespread weakness and paralysis. However, it’s not definitively established that the flu vaccine caused GBS in those instances.

Having a prior history of GBS doesn’t automatically preclude you from getting the flu vaccine. Discuss your specific situation with a healthcare provider to determine whether vaccination is appropriate.

Contact a doctor promptly if you notice symptoms of GBS after vaccination.

Who should get the flu vaccine?

The flu vaccine is generally recommended for everyone aged six months and older. Those at higher risk for severe influenza complications should also be vaccinated, including:

• pregnant individuals
• people aged 65 and above
• people with chronic medical conditions and their caregivers

The vaccine is not advised for people who:

• have had a prior allergic reaction to a flu shot
• have a severe egg allergy
• are currently ill with a moderate to high fever

Discussing with your clinician

The flu vaccine is considered safe and effective, with relatively few adverse effects. If you’re uncertain about getting vaccinated, consult a physician or pharmacist. They can guide you on whether the flu shot is suitable for you.

Questions to consider asking include:

• Is getting a flu vaccine advisable for me?
• Which flu vaccine option is most appropriate?
• Am I at high risk for serious flu complications?
• Am I more likely than others to experience vaccine side effects?

Q:

Can I receive a flu vaccine if I’m allergic to eggs?

A:

Many flu vaccines are produced using eggs, so they could potentially cause a reaction in people with egg allergies. Previously, the CDC recommended that people with egg allergies avoid the vaccine, but current guidance from the CDC indicates that most people with egg allergies can safely be vaccinated.

Whether you should get the vaccine depends on the severity of your egg allergy. If your reaction to eggs was limited to hives, you can receive any flu vaccine that is otherwise suitable. If your egg allergy caused more serious reactions — such as swelling or fainting — you should be vaccinated only in a setting with healthcare professionals prepared to manage an allergic reaction. Discuss vaccine options with your provider to choose a safe formulation.

Takeaway

Flu vaccine side effects are usually mild and brief, most commonly soreness or swelling at the injection location.

Experts commonly recommend an annual vaccination unless you have certain allergies or contraindications.

The flu vaccine is a safe, effective measure with relatively few side effects. If you’re unsure whether to get vaccinated, speak with a doctor or pharmacist who can help you determine if the flu shot is the right choice for you.