Jennifer Garner Puts Flu Shot in the Spotlight

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"But we don't reach anywhere near that," Edelman noted. "We have perhaps just one-quarter to one-third of Americans who get the flu shot."

One common myth: That if you don't get the shot by Thanksgiving, it's already too late. "It only takes about two weeks for the flu shot to become effective, so if the flu shot has just come to your neighborhood and will be around for a month or so, it still makes sense to get a flu shot," Edelman said.

Still, it's best to be prepared. "Immunization lasts about six months," Edelman said, "so earlier is always better, because you'll be protected, and you won't have to rush off when the flu hits your area." The flu season typically begins in the fall and peaks in February but can continue well though March.

Another myth: You can get sick from the flu shot. "A lot of people will get the flu shot and then maybe catch a cold, so they blame the flu shot for it, but they are not related," Edelman said. The shot itself is a standard injection in the arm, typically with little or no lingering soreness, he said.

Cain, who was set to get his own jab Monday morning at the event, agreed. "It doesn't really hurt," he said.

Getting immunized is not a guarantee that you won't get the flu, however, because each year scientists formulate the vaccine based on a highly educated guess of what influenza strains will dominate.

"The flu shot is probably about 85 to 90 percent effective in younger people, and in older people -- because their immune systems don't respond as well to the vaccine -- it may be closer to 65 percent effective," Edelman said. Still, "it's advisable to always get the flu shot, because there will always be at least partial immunity," he said.

On the other hand, the price of not getting vaccinated can be steep, especially for the very young or elderly. According to the lung association, 36,000 Americans die every year from influenza and about 226,000 are hospitalized. When combined with pneumonia, flu remains the eighth leading cause of death in the United States.