Millions of U.S. children are not getting the scheduled immunizations they need to ward off disease, experts warn.

"Despite the success of increasing the numbers of children being vaccinated, what is very troublesome is that 2.1 million children are not getting timely vaccinations," said Amy Pisani.

Pisani is executive director of Every Child By Two: The Carter/Bumpers Campaign for Early Immunization of Every Child By Two, which held a press conference on the issue Thursday.

The problem is particularly acute in the inner city, Pisani said. "Rates among African-American children are actually 13 percentage points lower than white and Hispanic children," she said. "This is due to insufficient funding from Congress," Pisani contended.

When children miss their immunization schedule, most can't catch up and are vulnerable to vaccine-preventable diseases, such as whooping cough, hepatitis, or meningitis and influenza.

One press conference participant described the advent of vaccines as one of the biggest health achievements of the 20th century.

Vaccinations have been very successful and resulted in the elimination of many childhood diseases, said Dr. Richard Judelsohn, a pediatrician at Buffalo Pediatric Associates and an advisor to the Erie County Department of Health, New York. "We want to make every effort never to let us slide back into a situation where we might begin to start to see [these] diseases again, diseases which have been eradicated," he said.

The schedule on which vaccines are given to children is carefully worked out, and takes into account expert opinions as to the best time to immunize against particular illnesses, Judelsohn explained. The schedule--devised by the U.S. Centers for Disease Control and Prevention's Advisory Committee on Immunization Practices--can be confusing, he admitted.

"It is a challenge for pediatric providers to navigate the schedule and all the associated tests that go with that," Judelsohn said. "And the parents feel this way, too," he added.

In the first two years of life, a child could get up to 24 injections, Judelsohn said. These include vaccines that prevent hepatitis A, hepatitis B, polio, influenza type B, measles, mumps, rubella, pneumonia, meningitis, diphtheria, tetanus and whooping cough. Often this complicated schedule results in delayed vaccinations, he said.

But delayed doses mean many kids aren't getting complete immunization during the recommended time period, Judelsohn said. "Delayed doses may result in under-protection, leaving the infant or child vulnerable to infection with a vaccine-preventable disease and its complications, or even death," he said.

Judelsohn believes that phone and e-mail reminders and recall systems can go a long way in making sure that vaccinations aren't missed. "Another thing that can be done is reducing the number of shots by using combination vaccines," he said.

Another conference participant, Dr. Gary Marshall, a professor of pediatrics at the University of Louisville School of Medicine, agreed that combination vaccines can go a long way toward insuring that children get the vaccinations they need when they need them.

"Fewer injections means less pain for the child, less anxiety for the mother, less anxiety for the nurse, and fewer doctor visits," Marshall said.

Moreover, combining vaccines may also have a medical benefit in reducing disease, according to some studies, Marshall said. "Hopefully, we will develop more data to support the idea that these combos have benefits beyond decreased pain and anxiety, and we may actually see benefits in terms of public health."

Another expert assured parents that vaccines are both safe and effective.

"If you look at the consequence of the diseases vs. the side-effects of the vaccine, the risk of the disease and its outcome is much greater," said Dr. Joseph Bocchini, a member of the Committee on Infectious Diseases of the American Academy of Pediatrics and chief of pediatric infectious disease at Louisiana State University Health Sciences Center, Shreveport.

"Vaccinations are one of the most important measures that parents can take to protect their children," he added.

Various groups have raised concerns that vaccines might be associated with other medical problems, Bocchini said. But these associations are almost always coincidental, he said.

"One of the difficulties with vaccines is that you give vaccines at a certain age to a large population of children, and it may be the same age when certain illnesses are likely to begin to appear," he said.

Bocchini noted that in some cases, a vaccine is given shortly before an illness develops, and a parent makes the association between the vaccine and the development of that illness. "In fact, they are occurring at the same time, but are not related," he said.

There has been ongoing controversy, for example, over a purported association between autism and the widely used measles, mumps, rubella (MMR) vaccine. "Autism begins to manifest itself in the second year of life," Bocchini pointed out. "Early in the second year of life is when we give the MMR vaccine. So, it wouldn't be unusual for a child to get the vaccine and then begin to show the signs of autism, and yet the two are not connected," he said.

Another vaccine expert cautioned that parents do need to get the facts on vaccines before they get their children inoculated.

"When parents are making a vaccination decision, they need to be really informed about the risks and complications of the disease and the vaccine," said Barbara Loe Fisher, the co-founder and president of the National Vaccine Information Center.

"You need to be clear about the contraindications to vaccines, know how to identify a vaccine reaction and make sure that doctors are cautious about proceeding with vaccinations after worsening health after a vaccination," Fisher said. "Parents should understand that vaccines do carry risks," she warned.