The most common side effects are mild and include soreness, redness or swelling where the injection was given. Headache, fever, aches, drowsiness, and tiredness may occur. You may have mild sweating and shivering as your immune system responds to the vaccine. This is not flu and will pass in a day or so.
Serious side effects such as a severe allergic reaction are rare.
In very rare cases Guillain-Barré syndrome (GBS) has been reported (Guillain-Barré Syndrome is a condition that affects the nerves in the body. It causes nerve inflammation and can result in pain, numbness, muscle weakness and difficulty walking). However, the risk of GBS following flu is significantly greater than that following the flu vaccine.