Flu shots are given to reduce the risk of falling ill after exposure to the influenza virus. It is possible to contract the flu virus after receiving the vaccine, but the illness is often milder than it would have been without the shot. In some cases, a person can contract a different strain of the flu than what is being vaccinated against. The common side effects of the flu shot are thought to be mild, and more serious hazards are rare. The Centers for Disease Control and Prevention (CDC) recommend the flu vaccine for nearly all individuals because the effects of the illness are greater than the most common side effects of the vaccine.
Minor Effects
The flu shot is administered into the muscle tissue, which can cause soreness that lasts up to two days. The administration site can become red or slightly swollen, but the CDC considers these to be mild side effects. A low-grade fever, hoarseness, cough or body aches are other minor effects of the vaccine. It is possible to develop red, itchy eyes that are sore soon after the vaccine is administered. Fever reducers or pain relievers can be used to help relieve these side effects, and none of them should persist much longer than two days.
Allergy
An allergic reaction to the flu vaccine can be life-threatening, but the CDC says it is a rare side effect. The reaction typically begins within a few minutes or hours of receiving the vaccine. Individuals with egg allergies should not be given the flu shot because it contains egg proteins from the manufacturing and growth of the virus. Symptoms to watch for include an elevated or persistent fever or behavioral changes. More prominent signs of allergy include trouble breathing, wheezing, hoarseness, hives, paleness, weakness or a rapid heart rate with dizziness. Any of these side effects of the flu vaccine require emergency medical attention.
Guillain-Barre Syndrome
Individuals who have ever had Guillain-Barre Syndrome (GBS) should discuss the risks of obtaining the flu vaccine with their doctor. The National Institutes of Health suggests vaccines can trigger the syndrome. GBS is a disorder of the body's immune system. The body begins attacking part of the nervous system, leading to weakness, tingling and partial to complete paralysis. In severe cases the individual may experience respiratory arrest.
