Mar. 23 -- FRIDAY, Aug. 31 (HealthDay News) -- Immunization programs in the United States have been remarkably successful, virtually eliminating diseases like measles and polio.

But experts are worried that cracks could be appearing in the public health system that would allow outbreaks of disease to occur even though vaccines are readily available.

That's because a sizable segment of the population -- the working poor -- makes too much money to qualify for federally funded vaccinations but has health insurance so meager that it won't cover some or any immunizations or booster shots. This is particularly true of new vaccines, the experts say.

As many as 2.1 million American children aren't getting timely vaccinations because of holes in the public health system, according to Amy Pisani, executive director of Every Child By Two: The Carter/Bumpers Campaign for Early Immunization of Every Child By Two. The campaign, co-founded by former First Lady Roslynn Carter, works with the U.S. Centers for Disease Control and Prevention to conduct educational programs for health-care providers.

"All these vaccines are being recommended but with hardly any funding whatsoever," Pisani said. "I foresee outbreaks."

Some experts believe those warnings will fall flat for some parents who desperately want to protect their children but can't afford to. There's no doubt that immunization has led to some of modern medicine's greatest triumphs over disease, those experts say.

"Overall, the vaccine program has been remarkably successful," said Dr. Joseph Bocchini, a member of the American Academy of Pediatrics' Committee on Infectious Diseases and chief of pediatric infectious disease at Louisiana State University Health Sciences Center, in Shreveport. "There has been a significant reduction in cases, as high as 99 percent in some diseases."

But that success could be challenged by a squeeze now facing some members of the working poor. Government assistance for immunization is dwindling at the same time that insurance companies are trimming their coverage for vaccinations, Pisani and Bocchini said.

Some diseases like whooping cough that are vaccine-preventable already are seeing a resurgence in parts of the country, Bocchini said.

The Section 317 Immunization Program is one of the tools the federal government uses to reach children of families who can't afford to protect their children, Pisani said. But the money for that program hasn't kept up with the growing number of vaccinations needed for children, she said.

In 1999, Section 317 funding allowed 747,000 American children to receive the full raft of recommended immunizations, according to a report to Congress filed by the CDC in April.

But, the report added, by 2006, the 317 program was only able to fully vaccinate an estimated 280,000 children. The report blamed the decrease on the rising cost of vaccines and the increased number of vaccinations in the routine childhood and adolescent schedule.

New recommended vaccinations include a booster shot for whooping cough, in an attempt to counter the disease's resurgence. Others include a new vaccination for meningitis and one for human papillomavirus, a vaccine that could radically diminish a young woman's chances of contracting cervical cancer later in life.

"We have new vaccines and no funding for it," Pisani said.

At the same time, insurance companies are slow to respond to these new vaccines, Bocchini said.

Some insurers don't even cover established vaccines, he said. "There are insurance policies that don't cover vaccines or, if they cover them, there is a co-pay, or it is part of the deductible," Bocchini said.

As the insurance companies trim their coverage, family doctors have to dip into their own pockets to help pay for vaccinations, he said.

"It's actually costing physicians to vaccinate people, because they aren't receiving adequate compensation for storing and administering the vaccines," Bocchini said. "Physicians have not been able to adopt new vaccines, because it would cost them too much."

In a child's first two years, he or she should receive as many as 24 injections. These include vaccinations for hepatitis A, hepatitis B, polio, influenza type B, measles, mumps, rubella, pneumonia, meningitis, diphtheria, tetanus and whooping cough.

Missing any one of these vaccinations could leave the child vulnerable to disease.

"One of the important things about immunization is it's important to stay on the schedule," Bocchini said. "If children's immunizations are delayed, that puts them at increased risk for exposure to vaccine-preventable disease."

Funding isn't the only reason a child's vaccination might be missed. Doctors also are looking at ways to simplify the complicated immunization schedule by combining some vaccinations, delivering in one shot what might earlier have required two or three or four visits to the doctor.

But Pisani said state governments need to stay constantly alert to disease and fund vaccination programs that will fill in when the federal government falls down.

"A lot of it has to do with political will, what is getting attention in that state," Pisani said. "It has to be a constant battle, because kids are being born every day."

More information

To learn more about childhood vaccines, visit the U.S. Centers for Disease Control and Prevention.

SOURCES: Amy Pisani, executive director of Every Child By Two: The Carter/Bumpers Campaign for Early Immunization of Every Child By Two, Washington, D.C.; Joseph Bocchini, M.D., member of the American Academy of Pediatrics' Committee on Infectious Diseases, and chief of pediatric infectious disease at Louisiana State University Health Sciences Center, Shreveport; U.S. Centers for Disease Control and Prevention, Atlanta