According to the Centers for Disease Control and Prevention (CDC), the flu shot is for anyone who wants to reduce their risk of getting the flu. In healthy adults, says the CDC, the shot can reduce the risk of flu by 70 to 90 percent. However, flu shots are also associated with certain risks.
Serious Allergic Reactions
Flu shots are uncommonly associated with serious allergic reactions including serum sickness, angioedema and, most serious of all, anaphylaxis. According to Medline Plus, serum sickness usually develops one to three weeks after exposure to the flu shot or other triggers and symptoms include fever, feeling sick, hives, itching, joint pain, rash, swollen lymph nodes and swelling of the arms, legs and face. Angioedema, according to the same source, presents as sudden swelling beneath the skin of the eyes, lips, hands, feet and throat. The swollen skin is characteristically pale and often itchy. Both serum sickness and angioedema can be life-threatening on their own when swelling results in airway constriction, or they can result in the most serious type of allergic reaction, anaphylaxis.
Anaphylaxis, according to Medline Plus, is a whole-body allergic reaction that is characteristically sudden and severe. Symptoms develop within seconds or minutes and may include abdominal pain or cramping, vomiting, diarrhea, difficulty breathing, anxiety, confusion, dizziness, fainting, slurred speech and heart palpitations. People with suspected anaphylaxis require emergency medical attention.
Due to the risk of severe allergic reactions, the flu shot is contraindicated in people with a history of hypersensitivity reactions to eggs, certain kinds of antibiotics and any other component of the vaccine. People with a history of life-threatening allergic reaction to the flu vaccine should not be re-vaccinated. According to Medline Plus, most reactions occur on the second exposure to an allergen with a few notable exceptions. One of these is the antibiotic polymyxin, which is used in the preparation of some kinds of flu shots; polymyxin has been known to cause an anaphylaxis-like reaction on first exposure.
Guillain-Barre Syndrome
Guillain-Barre (pronounced ghee-YAN bah-RAY) syndrome, or GBS, is an autoimmune disease in which a person makes antibodies against the coverings of the nerves. The onset of GBS is characterized by weakness and tingling sensations in the legs; the arm, trunk, and head are progressively involved. In some cases, a person may become paralyzed for weeks or months. According to the CDC, 5 to 6 percent of people with GBS die. Among survivors, recovery is prolonged (weeks to months) and residual weakness may persist for years.
GBS was first linked to the flu shot in 1976, when 1 in 100,000 people who received the swine flu shot developed the disease. Later, in 1992-1994, the seasonal flu shot appeared to confer an 1.7-fold increase in the risk of GBS. However, since approximately 1 in 1,000,000 people develop GBS each year, the risk amounted to less than one additional case per year. As of 2010, the CDC states that one person out of 1 million vaccinated persons may be at risk of GBS associated with the vaccine.
Other Adverse Events
The Food and Drug Administration (FDA) requires flu shot manufacturers to monitor adverse events in people who have received the vaccine. Because these events are reported voluntarily from a population of uncertain size, it is not always possible to reliably estimate their frequency or establish a causal relationship to the vaccine. Some of the conditions that have been reported include swollen lymph nodes, elevated heart rate, vertigo, conjunctivitis, eye irritation, eye pain, eye redness, eyelid swelling, abdominal pain or discomfort, nausea, chest pain, chills,
feeling hot, irritation of the nasal passages, irritation of the tonsils, seizures, dizziness, inflammation of the brain and spinal cord, facial palsy, facial loss of sensation, inflammation of the nerves, asthma, breathing problems, rashes and inflammation of the blood vessels.
