In 1977, there were over 500 cases of Guillain-Barr syndrome associated with a United States flu vaccination program. The cause of this outbreak was never discovered. Muscles that are controlled by nerves in the head may be involved. Muscle weakness near the involved nerves can be the most prominent sign. Deep tendon reflexes are decreased or absent.
People can have weakness of facial muscles and some muscles in the throat.
Some may have respiratory failure due to muscle weakness. These people need to have a breathing tube put in and be placed on a ventilator to help them breathe. Five percent of people die from respiratory failure. The severity of symptoms peaks by the second or third week. These symptoms overlap other syndromes such as botulism, thiamine deficiency, and myasthenia gravis.