Flu symptoms, according to the Centers for Disease Control and Prevention (CDC), include fever, head and body aches, cough, sore throat, runny or stuffy nose and sometimes diarrhea and vomiting. Unfortunately, some of the same symptoms can follow the seasonal flu shot. Compared to the flu, symptoms from the flu shot are short-lived--almost always resolving completely within two days--and mild--unlike the flu, they rarely interfere with normal activities.
Fever
The U.S. Food and Drug Administration (FDA) advises that fever, defined as oral temperature greater than 99.9 degrees F, occurs in approximately 1 percent of adults 18 and up. Fever is more common in children: 23 percent of children six months to three years and 16 percent of children three to nine years develop fever within seven days of receiving the shot. However, this figure includes many fevers that probably weren't related to the shot. In order to avoid underreporting, clinical trial participants were asked to report all fevers they experienced.
Head and Body Aches
"Harrison's Principles of Internal Medicine" says that pain--especially in the head, legs and lower back--is one of the most common symptoms of flu. Similar symptoms sometimes accompany the flu shot, however the prevalence varies by age, with older adults and younger children reporting the most pain symptoms. Among adults, according to the FDA, about 15 percent of adults over 65 experience head aches, body aches or both compared to 26 percent for adults between 18 and 65. Among children, caregivers reported pain in about 3 percent of children between six months and three years compared to 14 percent of children between three and nine years.
Diarrhea and Vomiting
The prevalence of vomiting, diarrhea and other gastrointestinal symptoms, such as nausea decreases with age. According to the FDA, in children between six months and three years, caregivers reported vomiting, diarrhea or both in up to 15 percent. In children between three and nine years, prevalence was about 8 percent. In adults, 1 percent of those between 18 and 65 and fewer than 1 percent of those over 65 vomited, although 9 and 3 percent, respectively, indicated they suffered from nausea. In children, researchers evaluated lack of appetite instead of nausea. Caregivers reported poor appetite in up to 24 percent of younger children and 8 percent of older children.
Cough and Other Respiratory Symptoms
Cough and other respiratory symptoms frequently occur in children--but not adults--after the flu shot. The most common problem is runny nose, observed in almost 50 percent of children six months to three years and 30 percent children three to nine years. Cough, sore throat, wheezing/shortness of breath, earache or some combination of these were also observed. However, like all of the symptoms described earlier, respiratory symptoms of the flu shot were also mild and brief.
References
- CDC: Flu symptoms and severity
- FDA: Influenza virus vaccine
- "Harrison's Principles of Internal Medicine, 17th edition;" A.S. Fauci, E. Braunwald, D.L. Kasper, S.L. Hauser, D.L. Longer, J.L. Jameson and J. Loscalzo (Eds.); 2008
