(HealthScoutNews) -- When it comes to child rearing, vaccinations are as routine as changing diapers and sleep deprivation.

Or so you'd think.

But as many as 25 percent of parents worry that the vaccines often mandated for their children to prevent diseases like measles, mumps and polio may be to blame for other unintended diseases, according to the Institute of Medicine..

Some parents have contended that the shots can cause everything from autism, hepatitis B and diabetes to neurological disorders and an impaired immune system.

That's just not true, health professionals say.

"Basically, there is no data to say there is an association between the vaccines and these diseases," says Dr. Margaret Rennels, a Maryland pediatrician who serves on the U.S. Centers for Disease Control and Prevention's Advisory Committee on Immunization Practices.

She cites an ongoing, three-year study of all research involving vaccinations and any associations with other diseases, which is being done by the institute, part of the National Academy of Sciences, an independent organization created by the federal government to advise on scientific and technical matters.

So far, the institute has issued three reports that found vaccinations were not linked to: autism; neurodevelopmental disorders, like attention deficit hyperactivity disorder and delayed speech; juvenile diabetes, pneumonia or meningitis. (A fourth report, examining any relationship between vaccines and hepatitis B and multiple sclerosis and other neurological diseases, is expected by early June.)

The bottom line: The institute stands behind the nation's current vaccination program.

"The committees, at the end of each of these reports, have said they don't recommend a policy review of the current schedule of vaccine use," says Dr. Marie C. McCormick, chairman of the institute's immunization safety committee, and a professor at Harvard University's School of Public Health.

However, the institute, citing a lack of data, does recommend further research into possible ties between vaccines and asthma, and whether certain people are genetically predisposed to respond poorly to certain shots.

Currently, infants receive up to 15 shots of five vaccines by the time they're 6 months old, and up to five additional shots of seven more vaccines by the age of 2, according to the institute. These shots protect against 11 diseases, including diphtheria, tetanus, whooping cough, measles, polio, and mumps.

Regulations for vaccinations are made at the state level, but most states adhere to similar regulations, Rennels.

The vaccines work by introducing into the body a weakened form of a bacteria or virus, like measles, so the immune system produces germ-fighting antibodies. These antibodies are then able to fend off any real virus or bacteria that might infect a child.

Rennels thinks some of the confusion about the effects of vaccinations has to do with timing.

"Autism, for instance, is [often] diagnosed when children start to talk, at about 1½ years," she says, "which is the same time they are getting a number of vaccinations."

It's understandable then, she adds, that a parent looking for causes of the condition might blame the vaccines.

"Parents need to know why," she says.

Rennels and other health professionals are concerned that parents worried about the perceived risks of vaccines might keep their children from being vaccinated against potentially fatal diseases.

"The bottom line is that the vaccines prevent diseases that are very real, that can harm people and kill them," she says. "If we don't maintain immunization levels, the diseases will come back. We have to weigh that against the theoretical concern for which there is no proof."

Dr. Anne Moscona, a pediatrics professor at Mount Sinai School of Medicine in New York City, adds: "Parents are concerned about autism, about neurological damage and the worry that their children will get more allergies if they are vaccinated. So we try to explain to them that the benefits of vaccinations far, far outweigh theoretical risks of harm from the vaccines."

What to Do: For more on the Institute of Medicine's immunization study, you can click here. To learn more about vaccines, visit the U.S. Centers for Disease Control and Prevention.

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