Infant Flu Shot Side Effects

For the 2009-2010 flu season, the Food and Drug Administration approved two vaccines, Fluria and Fluzone, for administration in infants six months and older. No vaccine is approved for administration in infants younger than six months. As with adults, the infant flu shot is frequently associated with side effects you may wish to consider in scheduling your baby for vaccination.

Doctor giving a baby a flu shot. (Image: didesign021/iStock/Getty Images)

Injection Site Reaction

In infants, it is recommended that the flu shot be administered on the front outside of the thigh. In clinical studies for Afluria, injection site reaction was actually less common among younger children compared to older children. Among children six months to three years old, pain, redness and swelling were observed in 37, 38, and 21 percent respectively. While redness and swelling are usually obvious, pain in infants is more difficult to identify and may be evidenced by fussiness, irritability and favoring the opposite extremity.

Flu-Like Illness

In both adults and children, the flu shot is frequently associated with a flu-like illness. Compared to the true illness, symptoms are usually mild and brief. However, parents may want to consider this side effect in determining the appropriate time to schedule vaccination for their infants. In clinical studies for Afluria, the most frequent symptoms in children under three were: runny nose (48 percent), irritability (48 percent), cough (32 percent), loss of appetite (24 percent), fever--defined as oral temperature greater than 101.3 degrees F or underarm temperature greater than 99.4 degrees--(23 percent), vomiting or diarrhea (15 percent), generalized muscle pain (9 percent), sore throat (5 percent), headache (3 percent), muscle pain (3 percent) and ear ache (3 percent). In terms of severity, 78 percent of symptoms were rated by parents as mild, 19 percent were moderate and 3 percent were severe. Severe fever, defined as oral temperature greater than 104 degrees F or underarm temperature greater than 103.1 degrees F, was observed in less than 1 percent of children.

Anaphylaxis

Anaphylaxis is a life-threatening allergic reaction that is a recognized complication of the flu shot. Symptoms of anaphylaxis in adults and children, according to the American College of Allergy, Asthma and Immunology, include trouble breathing, hives or swelling, tightness of the throat, hoarse voice, vomiting, abdominal pain, diarrhea, low blood pressure and rapid heartbeat that may progress rapidly to cardiac arrest and death. Anaphylaxis occurs on or after the second exposure to an allergen. Since infants receive two flu shots on separate occasions, anaphylaxis is theoretically more likely to follow the second injection.

Encephalomyelitis

Acute disseminated encephalomyelitis (ADE) is a rare but severe side effect of the flu shot and several other vaccines including rabies, diptheria and polio. According to a 2008 study in the Journal of Clinical Neuroscience, ADE usually occurs in children, including infants. ADE typically presents with abrupt onset of fever, muscle weakness, increased or decreased reflexes, vision changes, impaired balance and other symptoms within three months of vaccine administration. Fever usually resolves within a few weeks; however, neurological deficits persist for months and even years. ADE is extremely rare and is believed to involve an interaction between the flu shot and a person's immune system.

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