WASHINGTON -- The Institute of Medicine says getting up to 20 vaccinations by the age of 2 does not increase a child's risk of developing diabetes or various infections.

However, there is not enough evidence yet to decide if multiple shots increase the risk of developing asthma, the panel of independent scientists concluded.

The report issued Wednesday should reassure parents that "there's not a lot of support for those risks" critics often cite, said the panel chairwoman, Dr. Marie McCormick of the Harvard School of Public Health. But "the diseases that their children are being protected against are very real."

The report is one of a series on the health effects of immunization, compiled by an institute-appointed committee of medical specialists who have no financial or advisory connections with vaccine manufacturers. The Institute of Medicine is an independent organization that does research at the request of the government.

Recent surveys suggest about 25 percent of parents worry that infants get so many vaccines that the shots could overwhelm their immature immune systems and cause infections or immune-related disorders such as Type 1 diabetes.

In 1980, babies were immunized against four diseases. Today, by age 2 most children have had up to 20 shots to protect against 11 diseases.

But babies actually are exposed to fewer antigens -- foreign substances that trigger an immune response -- now than in previous decades, the institute said. For example, pertussis vaccine given in the 1980s contained about 3,000 potential antigens, while a safer version introduced in the '90s has about five. Today's hepatitis B vaccine has only one antigen; smallpox shots given until 1971 had 200.

In fact, research suggests the capacity of the infant immune system is at least 1,000 times greater than what is required to respond to immunization.

"It really is fully competent. It has to be -- you're dealing with all sorts of bugs" from birth, McCormick said.

Also, numerous studies show multiple shots do not increase the incidence of Type 1 diabetes or such infections as colds, ear infections, pneumonia or meningitis, the panel concluded.

However, some studies suggest certain vaccines might increase the risk of allergic disorders such as asthma, while others find no link. So the panel concluded there is insufficient evidence to decide if asthma could be linked to multiple shots.

Still, many other factors play a role in who gets asthma, so the conflicting studies suggest that even if the shot risk is real, it's not large, McCormick said. Thus, "on balance, we would recommend immunization."

But parents need more clear, scientific information about vaccine risks and benefits, the panel said, urging the government to form a task force to ensure that happens.

There already is such a group, but health officials will consider whether it needs improvement, said Health and Human Services spokesman Bill Hall.

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