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Medical Author:

Melissa Conrad Stöppler, MD

Melissa Conrad Stöppler, MD

Melissa Conrad Stöppler, MD, is a U.S. board-certified Anatomic Pathologist with subspecialty training in the fields of Experimental and Molecular Pathology. Dr. Stöppler's educational background includes a BA with Highest Distinction from the University of Virginia and an MD from the University of North Carolina. She completed residency training in Anatomic Pathology at Georgetown University followed by subspecialty fellowship training in molecular diagnostics and experimental pathology.

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Medical Editor:

William C. Shiel Jr., MD, FACP, FACR

William C. Shiel Jr., MD, FACP, FACR

Dr. Shiel received a Bachelor of Science degree with honors from the University of Notre Dame. There he was involved in research in radiation biology and received the Huisking Scholarship. After graduating from St. Louis University School of Medicine, he completed his Internal Medicine residency and Rheumatology fellowship at the University of California, Irvine. He is board-certified in Internal Medicine and Rheumatology.

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In this Article

• Flu vaccine (flu shot) facts
• What is flu?
• Why vaccinate for the flu?
• What are the different types of flu vaccines?
• What flu viruses does the flu vaccine protect against?
• How does the flu vaccine work to prevent the flu?
• When should one receive the flu vaccine?
• Who should receive the flu vaccine?
• Who should not receive the flu vaccine?
• What are risks and side effects of the flu vaccine?
• Can the flu vaccine give me the flu?
• What should I do about adverse reactions to the flu vaccine?
• How effective is the flu shot?
• What was the novel H1N1 (swine flu) vaccine?
• What is the best way to locate a flu shot clinic?
• Patient Comments: Flu Vaccination - Side Effects
• Flu Vaccination Index

Who should not receive the flu vaccine?

Those who should avoid the flu vaccine include

• people who have ever had a severe allergic reaction to eggs;
• people who have ever had a severe allergic reaction to influenza vaccine;
• people with a history of Guillain-Barré syndrome (a severe paralytic illness, also called GBS) that occurred after receiving influenza vaccine and who are not at risk for severe illness from influenza should generally not receive vaccine;
• people under 65 years of age should not receive the high-dose flu shot;
• people who are under 18 years old or over 64 years old should not receive the intradermal flu shot.
• If you are sick with a fever when you go to get your flu shot, you should talk to your doctor or nurse about whether or not you should get your shot at a later date. However, you can get a flu shot at the same time you have a respiratory illness without fever or if you have another mild illness.

What are risks and side effects of the flu vaccine?

Serious side effects of the flu vaccine are uncommon. Side effects of the injection vaccine include soreness at the site of the injection, muscle aching, fever, and feeling unwell. People report less discomfort with the intradermal rather than the intramuscular vaccine. Very rarely, serious allergic reactions have been reported.

Guillain-Barré syndrome (GBS) is an illness characterized by fever, nerve damage, and muscle weakness. In 1976, vaccination with the swine flu vaccine was associated with development of GBS. Studies have been done to evaluate if other flu vaccines were associated with GBS, with only one of the studies showing an association. That single study suggested that one person out of 1 million vaccinated people may be at risk of GBS associated with the vaccine.

The live viruses in the nasal-spray vaccine are weakened so that they do not cause severe symptoms. However, people at high risk for serious complications of the flu (see above) and those with suppressed immune systems (including those taking biologic medications, such as for rheumatoid arthritis) should receive the inactivated rather than the nasal-spray vaccine. Mild symptoms can occur as a side effect of the vaccination. Side effects of the nasal-spray flu vaccine can include runny nose, headache, sore throat, and cough. Children who receive the vaccine may also develop mild fever and muscle aches.