Common Side Effects of the Influenza Vaccine

The influenza vaccine provides protection against the annual flu, which is why millions of people get the flu shot each year. While very few serious side effects have been reported, many people experience mild side effects to the flu shot (intramuscular injection) or nasal spray flu vaccine.

The most common side effects reported are injection site reaction, low-grade fever, headache, and muscle aches. Despite a common myth that getting the flu shot can give you the flu, the vaccine will not infect you with influenza.

There are three different formulations of flu vaccines:

• Inactivated vaccines contain flu viruses that have been inactivated or killed and are therefore not infectious.
• Recombinant vaccines use only a single gene from a flu virus, as opposed to the full virus, to produce an immune response without causing an infection.
• Live attenuated influenza vaccines (LAIV) are used in the nasal spray (FluMist Quadrivalent). This vaccine uses a live virus, however, it has been weakened and will not cause influenza illness. The attenuated virus is cold-adapted and can only multiply at cooler temperatures, like those in the nose biome, and cannot survive at body temperature.

The side effects you may experience from the flu shot are due to a mild immune system response that boosts your immunity against the full flu.

Side effects of the influenza vaccine are typically mild. Though rare, allergic reactions including anaphylaxis may occur. If you are having trouble breathing following a flu shot, get medical attention immediately. People who are allergic to eggs are a high risk of reaction and should discuss alternatives with their doctor.

• Pain at the injection site
• Redness and swelling at the injection site
• Headache
• Fatigue or malaise (feeling tired)
• Red or itchy eyes
• Hoarse voice
• Cough
• Fever

• Runny nose, congestion, or cough
• Fever
• Headache or muscle aches
• Wheezing (typically in children)
• Abdominal pain or occasional vomiting or diarrhea (typically in children)
• Sore throat
• Weakness or fatigue (feeling tired)