The flu is a contagious respiratory disease that produces a spectrum of sickness ranging from cold-like symptoms to fatal pneumonia, according to the Centers for Disease Control and Prevention (CDC). The flu shot can reduce flu risk by 70 to 90 percent in healthy adults. However, like the disease, the flu shot is associated with a spectrum of complications that range from mild to severe. Knowing these complications can help you and your doctor decide whether vaccination is right for you.
Injection Site Reaction
Up to 60 percent of adults and children who receive the flu shot complain of an injection site reaction. In clinical studies by the makers of Afluria, a 2009-2010 FDA-approved seasonal flu vaccine, the most common symptoms were tenderness (60 percent); muscle pain (40 percent); redness (16 percent); swelling (9 percent); and bruising (5 percent). In most cases, symptoms were rated as mild. Less than 1 percent of symptoms were rated as severe.
Flu-Like Illness
In clinical studies by the makers of Agriflu, almost 25 percent of adults who received it or another flu shot complained of systemic, flu-like illness after receiving the vaccine. The most common symptoms were headache (22 percent); generalized muscle pain (19 percent); malaise (12 percent); fatigue (9 percent); chills (8 percent); joint pain (6 percent); sweating (4 percent); and fever over 101.3 degrees F (3 percent). Children reported a broader range of symptoms including irritability, rhinitis, fever, cough, loss of appetite, vomiting, diarrhea, headache, muscle aches and sore throat. In 99 percent of cases symptoms were mild to moderate. In 96 percent of cases, symptoms began within four days of vaccine administration. An additional 4 percent of patients developed symptoms up to three weeks later.
Anaphylaxis
In very rare cases, the flu shot can trigger a life-threatening allergic reaction known as anaphylaxis. The symptoms of anaphylaxis are present within seconds or minutes of vaccine administration and, according to Medline Plus, include breathing problems, abnormal heartbeat, nausea, vomiting and/or abdominal pain, hives or skin redness and mental confusion or unconsciousness. People with symptoms of anaphylaxis need to be taken to the emergency department without delay. Anaphylaxis is often associated with allergies to eggs or the antibiotics neomycin, kanamycin, polymixin B and gentamicin, according to Agriflu product literature. People with documented hypersensitivity to these components or prior history of anaphylaxis related to the flu shot should not be vaccinated.
Guillain-Barre Syndrome
Guillain-Barre Syndrome (GBS) is an autoimmune disorder in which the body makes antibodies against the coverings of the nerves. One in 100,000 people who received the swine flu vaccine in 1976 and one to two per million people who received the seasonal flu vaccine between 1992 and 1994 developed GBS and the FDA required all 2009-2010 flu vaccine manufacturers to include this risk on their product literature. GBS initially presents with muscle weakness and tingling which progresses to ascending paralysis. When paralysis reaches the level of the diaphragm, a person will require mechanical ventilation to prevent respiratory failure (suffocation.) GBS is fatal in 5 to 6 percent of people, despite supportive care. Among survivors, nearly one-third report persistent weakness after three years.
