Kids routinely get vaccinated at ages 2 months, 4 months, 6 months, 1 year and 15 months. They also receive vaccines between the ages of 4 and 6 and again around age 12, says Dr. Terrence Steyer, associate professor of Family Medicine at the Medical University of South Carolina.

Vaccines prevent children and adults against severe disease states and against complications from common infections, he says.

"For example : diseases like polio and diphtheria are almost totally eliminated from the world."

To create a vaccine, doctors first make antigens, which are little pieces of a molecule of the germ being immunizing against.

To make an antigen, the bacterium, or single-celled organisms, are killed and chopped up into little pieces. Small amounts of additives and preservatives are then added to keep the vaccine from contamination.

"You can't make a vaccine or much of anything else without putting a preservative in it. [It's] the same types of preservatives that you get in all kinds of foods and things," says Dr. Stephen Worsham of Charles Towne Pediatrics. "You get a whole lot more of them when you eat a Twinkie than you do when getting vaccinated. There is no evidence that any of them are harmful."

When injected, the body recognizes and reacts to the vaccine and makes antibodies, which help protect against disease.

Currently, researchers are working on combining vaccines so that the number of shots can be reduced.

The most common side effects are pain at the injection site, local redness and occasional fevers. More serious side effects, such as infection, seizures and serious allergic reactions, are relatively uncommon.

"There has been a great deal of lay press about the relationship between vaccines and autism. No scientific studies have confirmed an association," Steyer says.

Thimerosal, a preservative theorized by some to cause autism, was removed from the routine children's vaccines in 2001.

"Nobody ever had any problem with it when it was in the vaccines," Worsham says. "There was not a single incident of anyone ever having a problem reaction or poisoning from mercury or thimerosal when they were in. They were taken out simply because mercury can be toxic and because of the theoretical possibility of it."

Want to know more?

• vaers.hhs.gov

The Vaccine Adverse Event Reporting System, a national vaccine safety surveillance program co-sponsored by the Centers for Disease Control and Prevention and the Food and Drug Administration

• www.cdc.gov/vaccines

• Centers for Disease Control and Prevention