As summer gives way to fall, flu season is sure to follow. The Centers for Disease Control and Prevention recommends that all adults and children older than 6 months get a yearly flu vaccine because it’s the best way to avoid catching the flu. Flu vaccines come in two forms, a nasal spray and a shot. Several different flu shots are available to choose from. While flu shots are generally safe and effective, side effects are possible, as with any medicine. Minor side effects, such as soreness at the injection site, are most common. Rare side effects include allergic and nervous system reactions.
Injection Site Soreness
The most common side effect experienced by people receiving the flu shot is soreness at the injection site. According to the World Health Organization, studies have shown that 10 percent to 64 percent of people who get flu shots experience sensitivity or soreness at the site of injection. This is usually mild and goes away in a day or two. Injection-site soreness is more commonly reported by women than men. It is also more common with high-dose flu shots that are given to adults 65 and older, compared to standard-dose flu shots.
Fever and Other Generalized Symptoms
Flu shots stimulate the immune system, which sometimes causes generalized symptoms such as a low fever, feeling a bit tired, achiness and headache. Young children and older adults most commonly experience these symptoms. The WHO reports that up to 12 percent of children under 5 years old experience a mild fever for a day or two after a flu shot, but only 6 percent of children 6 to 15 experience this side effect as it becomes less common with age. Healthy young adults rarely experience fever or other generalized symptoms from a flu shot, but adults 65 and older sometimes do.
Oculorespiratory syndrome is an uncommon side effect of flu shots. Possible symptoms include eye redness; swelling of the eyes, face or lips; and airway-related symptoms such as a sore throat, wheezing, chest tightness or difficulty breathing or swallowing. Symptoms range from mild to severe. They typically develop 2 to 24 hours after receiving a flu shot and go away within 48 hours. Oculorespiratory syndrome is more common in women than men and most often occurs in people aged 40 to 59. The cause remains unknown but may relate to flu vaccine manufacturing processes. This type of reaction affects approximately 76 out of every million people who get a flu shot, according to the WHO.
Guillain-Barré syndrome is a rare condition in which the immune system mistakenly attacks the nerves of the body. It typically begins with weakness or tingling in the legs, which may spread upward to affect the trunk and arms. In severe cases, temporary paralysis can occur. The cause of Guillain-Barré syndrome is not known, but it most often occurs after a viral infection. Rare cases have also been reported after an immunization, such as a flu shot. Guillain-Barré syndrome can affect people of any age. The WHO notes that the syndrome occurs in roughly 1 or 2 individuals out of every million who receive a flu shot.
Flu shots sometimes cause an allergic reaction in people who are sensitive to ingredients in the vaccine. These are usually mild, such as hives, but can rarely be severe -- a condition known as anaphylaxis. Most flu shots are prepared by growing the virus in eggs, and minute amounts of egg protein can sometimes trigger a reaction in people who are highly allergic. However, the CDC reports that most people with an egg allergy can safely receive a flu shot. People with gelatin or certain antibiotic allergies may also react to a flu shot. However, according to the WHO, those who receive a flu shot and experience a severe allergic reaction number less than 1 person for every million.
- Centers for Disease Control and Prevention: Vaccination: Who Should Do It, Who Should Not and Who Should Take Precautions
- World Health Organization: Observed Rate of Vaccine Reactions: Influenza Vaccine
- Centers for Disease Control and Prevention: Prevention and Control of Seasonal Influenza with Vaccines: Recommendations of the Advisory Committee on Immunization Practices (ACIP) — United States, 2014-15 Influenza Season
- Centers for Disease Control and Prevention: Inactivated Influenza VIS, Provider Information
- World Health Organization: Weekly Epidemiological Record (Jan. 24, 2003)
- National Institute of Neurological Disorders and Stroke: Guillain-Barré Syndrome Fact Sheet
- Center for Disease Control: Vaccines and Autism: A Summary of CDC Conducted for Sponsored Studies
- Centers for Disease Control and Prevention: Prevention and Control of Seasonal Influenza with Vaccines: Recommendations of the Advisory Committee on Immunization Practices — United States, 2013-2014
- Public Health Agency of Canada: Oculo-Respiratory Syndrome Following Influenza Vaccination: Review of Post-Marketing Surveillance Through Four Influenza Seasons in Canada