What are the side effects of the flu vaccine?

Common side effects of the flu vaccine include soreness at site of vaccination, headache, fever, nausea, and muscle aches.

The flu vaccine protects against three or four strains of influenza. Every year, with a few exceptions, the composition of the vaccine changes to protect against the current most common or most deadly circulating flu viruses.

Most adults develop antibody protection against these viruses within two weeks of vaccination. Routine annual vaccination is advised by the Advisory Council on Immunization Practices (ACIP) for everybody aged six months or older without contraindications to the vaccine.

The most common side effects of the flu vaccine are:

• A headache or a migraine
• Abnormal crying
• Changes in appetite
• Chest tightness
• Difficulty moving
• Drowsiness
• Fever
• Flu-like illness
• Gastrointestinal effects (nausea, diarrhea, vomiting)
• Injection site reactions (such as pain, redness, bruising, or swelling around the injection site)
• Irritability
• Muscle, joint, or back pain
• Nasal congestion
• Reddened eyes
• Tiredness/lethargy.

Severe allergic reactions to the flu vaccine are rare. People with a history of fainting after any vaccine should sit or lie down for 15 minutes following a flu vaccination.

Related: How well does the flu vaccine work?