Flu is a contagious respiratory disease caused by the influenza virus. Each year, according to the Centers for Disease Control and Prevention (CDC), more than 200,000 people in the United States are hospitalized for the flu and 36,000--mostly elderly people--die. The single best way to prevent seasonal flu, the CDC advises, is to get a seasonal flu vaccination each year. However, the flu shot is associated with risks and side effects you may wish to consider in deciding when and whether to get vaccinated.
Injection Site Reaction
The most common side effect of the flu shot is an injection site reaction. In clinical studies by the makers of the FDA-approved flu shot Afluria, the most symptoms were tenderness (60 percent), pain (40 percent), redness (16 percent), swelling (9 percent) and bruising (5 percent). In most cases, these symptoms lasted less than two days. For 99 percent of people, symptoms were "mild" or "moderate" with the designation of "severe" reserved for symptoms that were bad enough to interfere with activities. The flu shot also carries a small risk of injection site complications including abscess and cellulitis (infection of the skin).
Flu-Like Illness
Some people report mild flu-like illness as a side effect of the flu shot. In clinical testing for the FDA-approved flu shot FluLaval, manufacturer GlaxoSmithKline reported the most common flu-like symptoms were headache (18 percent), fatigue (17 percent), muscle pain (13 percent), fever (11 percent), malaise (10 percent), sore throat (9 percent), red eyes (6 percent), cough (6 percent) and chills (5 percent). Most symptoms were rated as "mild" or "moderate." In almost all cases, symptoms resolved in two days or less. The elderly were slightly less likely to report these symptoms. Children experienced symptoms at rates similar to adults; however, more diverse symptoms including irritability, nasal irritation, loss of appetite, vomiting and diarrhea were described in children.
Allergic Reactions
The flu shot is associated with the risk of an allergic reaction. In the Dec. 4, 2009, edition of "Morbidity & Mortality Weekly Report," the CDC indicated that 16 "serious allergic reactions" and 18 confirmed cases of anaphylaxis had been reported out of approximately 145.1 million administered doses of seasonal and H1N1 flu vaccine. Anaphylaxis is a life-threatening allergic reaction that usually presents with seconds or minutes of exposure to the flu shot or other allergen. Symptoms of anaphylaxis, according to MedlinePlus, include trouble breathing, hives or skin rashes, hoarse voice, tight throat, vomiting, diarrhea, abdominal pain, low blood pressure, a sense of doom and cardiac arrest. People with allergies to eggs, antibiotics, natural rubber latex or a history of previous life-threatening allergic reaction to the flu shot should share this information with their health care provider before being vaccinated.
Guillain-Barre Syndrome
The flu shot also is associated with the risk of an autoimmune disease known as Guillain-Barre (pronounced ghee-YAN bah-RAY) syndrome, or GBS. People with GBS make antibodies against the coverings of their peripheral nerves. The hallmark of GBS is ascending paralysis that begins in the legs and spreads to the arms, trunk and sometimes the head. While paralysis is not permanent, recovery often is prolonged (weeks to months), with some people complaining of residual symptoms as long as three years later. A link between GBS and the flu vaccine first was identified in 1976, when one in 100,000 people vaccinated for the swine flu developed GBS. The vaccine since has been reformulated; however, the CDC still estimates that the flu shot may cause one additional case of GBS per million people vaccinated.
