What the flu vaccine can and can't do

Our doctor has recommended a flu shot for our toddler with asthma. Does the flu shot protect us against common stomach flu bugs or just respiratory bugs?


Robert Steele

Robert W. Steele, MD, is a board certified pediatrician at St. John's Regional Health Center in Springfield, MO. He graduated from medical... Read more

The term "flu" has taken on a meaning in the English language to mean any common viral illness. If a child gets a runny nose, sore throat, cough, or nasal congestion, then he has a "touch of the flu." If he gets diarrhea, then he has an "intestinal or stomach flu." We have all used the term to describe these common infections much like how we use the name Kleenex to describe any type of facial tissue or Band-Aid for any type of adhesive bandage. But while the term, flu, is a convenient way to summarize common cold symptoms, it makes understanding what the actual flu vaccine is more difficult.

The real flu is the disease caused by the influenza virus. The symptoms of the flu include a fever, congested head, runny nose, muscle aches and pains, but they vary from person to person. However, the flu can become more serious by causing more serious problems such as pneumonia and even death. There are two strains of this virus, influenza A and influenza B. And for each of the two strains, there may be several subtypes that cause disease. The majority of flu outbreaks in the United States are caused by influenza A. And the flu vaccine, which is customized each year, carries the three types of flu (usually two types from the A strain and one from the B strain) which scientists at the Centers for Disease Control in Atlanta feel will cause the majority of flu infections for the year.

The vaccine is not foolproof. It is effective in about 90 percent of those who receive it. In addition, the immunity to the flu lasts only about four months. The flu season, on the other hand, lasts about five to six months. What this means is that a certain percentage of those who get the vaccine will still get the flu simply because they didn't respond to the vaccine. In addition, if one gets the vaccine early in the season and the flu happens to roll through town late in the season, immunity may have decreased enough to become ineffective in fighting the infection.

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