There are several flu vaccines available to help people protect themselves against the seasonal flu and H1N1 (swine flu) virus. According to the Centers for Disease Control (CDC), the risk of severe harm from the flu shot is minimal, and any side effects that do occur--for example, low-grade fever, aches and skin redness around the injection--are likely to be minor and temporary. There are reports, however, of more serious reactions, including allergic reaction and the onset of various medical conditions.
Allergic Reaction
Allergic reactions can happen after vaccination with the seasonal flu or H1N1 vaccine. Symptoms typically develop quickly, from a few minutes to a few hours after getting the vaccination. Flu vaccines are grown in eggs, and the final vaccine may contain egg protein. Those with chicken egg allergies (and those who have had allergic reactions to vaccines in the past) are advised not to get influenza vaccinations to avoid an allergic reaction.
Those who do have allergic reactions can have symptoms such as wheezing, skin rash, rapid heart rate, difficulty breathing, hoarseness and wheezing, weakness, pale skin and dizziness. There are reports among those receiving vaccination with the H1N1 vaccine (monovalent injection and intranasal forms) of immune system responses and hypersensitivity reactions, including anaphylaxis (sudden drop in blood pressure and problems breathing), facial swelling and hives.
Guillain-Barré syndrome (GBS)
Guillain-Barré syndrome (GBS) is a disorder characterized by muscle weakness or paralysis. The immune systems of people with GBS attack and damage their nerve cells, causing symptoms that can last weeks or months or sometimes permanently. According to the Centers for Disease Control, vaccinations may activate the immune systems of certain people, causing the onset of GBS. It is not currently understood exactly how vaccines cause this to happen.
Bell's Palsy
The seasonal flu and H1N1 influenza vaccines have been linked to the onset of some medical conditions and symptoms. It is as yet unclear whether the flu vaccines caused these symptoms directly or whether some other factors contributed to their onset. For example, the 2009 H1N1 monovalent vaccine, the intranasal H1N1 vaccine and some seasonal flu vaccines have been linked to a nervous system disorder called Bell's palsy--a condition in which the facial muscles become paralyzed on one side. In many cases, these symptoms are only temporary.
Other neurological disorders such as optic neuritis or neuropathy (damage to the optic nerve that can lead to blindness), myelitis (inflammation of the spinal cord that affects the brain and limbs), brachial neuritis (weakness and pain in the shoulder due to acute nerve damage) and convulsions have also been reported.
Other adverse events that have been reported following influenza vaccination include vasculitis (inflammation of the blood vessels), epistaxis (nosebleed), dyspnea (shortness of breath), rash and gastrointestinal reactions such as nausea, diarrhea or vomiting.
