The flu is a contagious respiratory infection caused by the influenza virus. Each year, according to the Centers for Disease Control and Prevention (CDC), flu affects 5 to 20 percent of Americans and causes over 200,000 hospitalizations and 12,000 deaths. Getting a seasonal flu vaccination can reduce your risk of getting the flu by 70 to 90 percent. However, the flu shot is sometimes associated with adverse effects you may wish to consider.
Injection Site Reaction
The most common adverse effect of the flu shot is a reaction at the injection site. In clinical studies by the makers of Agriflu, mild to moderate injection site pain was reported by 30 percent of flu shot recipients. Other, less common symptoms included redness, swelling and bruising. One percent of people reported symptoms that were severe enough to interfere with daily activities. In most cases, symptoms resolved within one or two days.
Flu-Like Illness
Transient, flu-like symptoms are another common adverse effect of the flu shot. In clinical testing for Fluvirin, the most common symptom was headache (30 percent), followed by muscle pain (21 percent), malaise (19 percent), fatigue (8 percent), sore throat (8 percent), chills (7 percent), nausea (7 percent), joint pain (7 percent), sweating (6 percent), cough (6 percent), chest tightness (1 percent), wheezing (1 percent) and other breathing problems (1 percent). Symptoms were more common in younger adults compared to adults over 65. More diverse symptoms are reported in children, including irritability, runny nose, vomiting and diarrhea. In almost all cases, symptoms begin within 72 hours of receiving the shot and resolve completely within one or two days.
Guillain-Barre Syndrome
Guillain-Barre syndrome (GBS) is an neurological disorder that is an uncommon complication of the flu shot. Early symptoms, according to the National Institute of Neurological Disorders and Stroke (NINDS), include weakness and tingling in the legs. Over the course of a few weeks, symptoms may spread to the arms, trunk and head and often increase in severity to the point that the affected person is completely paralyzed. GBS is fatal in 5 to 6 percent of cases. Most people recover, but the process can take months, even years. As many as 30 percent of people report lingering weakness three years later, notes NINDS. The CDC estimates the risk of GBS due to the flu shot at about one case per million people vaccinated.
Allergic Reactions
Allergic reactions are occasionally reported in people who receive the flu shot. In fact, according to the flu shot prescribing information, certain kinds of allergies are the only absolute contraindication to receiving the shot. Allergic reactions range in severity from hives (wheals) and itching to more serious syndromes such as angioedema and anaphylaxis. The main symptom of angioedema is sudden swelling that, unlike the swelling associated with hives, occurs below the skin. In some cases, swelling may affect the airways and interfere with breathing. Angioedema can also progress to the most feared allergic reaction, anaphylaxis.
Anaphylaxis, according to MedlinePlus, is a severe, life-threatening allergic reaction involving the entire body. Initial symptoms may include abdominal pain/cramping, breathing problems, mental confusion, fainting, light-headedness, dizziness, hives or itchiness, heart palpitations and a feeling of doom. Without immediate medical attention, cardiac or respiratory failure and death may result. In the December 4, 2009, edition of Morbidity & Mortality Weekly Report, the CDC announced 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.
