The majority of side effects from the vaccines are mild. The live-virus nasal flu vaccine has a risk of giving you a runny nose and congestion as well as a fever and muscle aches. This makes sense because you are getting a weakened form of the virus and you might get a mild influenza infection. The injectable version of the vaccine can occasionally cause a sore arm or swelling and redness at the injection site.
A different version of the flu vaccine was linked to Guillain-Barré syndrome (GBS) during the 1970s. The current version is not linked to GBS. However, as a precaution, people who have had GBS should discuss the risks and benefits of the vaccine with their doctor.