Vaccination is considered the most effective medical technology ever devised. In the industrialized world, vaccines have wiped out potentially deadly and disabling diseases, such as tetanus and diphtheria. Poor countries have not faired as well, but during the past two decades a concerted international campaign to reach children worldwide has saved millions of lives.

Every day in thousands of clinics around the world, health workers give life-saving vaccines to young patients. Nowadays, immunizations have become almost routine. But that was not always the case. In the 1970s, the U.N. Children's Fund UNICEF reports, barely 10 percent of children under age five in the developing world were vaccinated against six preventable killer diseases. At that time, it was common for children to die from measles, whooping cough, and other preventable illnesses, says Eric Laroche, UNICEF deputy director for emergency.

"What is really, I would say, very peculiar to the death of children is it is always in silence," he said. "It is never dramatic in a media sense, if I may say. And I have seen children literally dying in the arms of their mothers, without even the mother noticing that they were dying."

In the 1980s, aid agencies made a major push to get children immunized against vaccine-preventable diseases. They promoted the benefits of immunization through intensified information and education campaigns in villages and communities around the world. These campaigns paid off. UNICEF says coverage against childhood diseases increased to nearly 80 percent.

But this dramatic increase in global immunization coverage leveled off in the 1990s. In several African nations, rates even dropped to less than 30 percent. UNICEF estimates about 34 million infants - about one-quarter of the children born every year - are not protected against diseases for which inexpensive vaccines are available.

World Health Organization communicable diseases expert David Heymann says vaccines have been crucial in controlling diseases in children. "The only vaccine-preventable disease that figures among the top killers in infectious diseases today is measles," said Dr. Heymann. "And measles is rapidly decreasing as immunization coverage for measles increases."

Dr. Heymann led WHO's program to stop Severe Acute Respiratory Syndrome, or SARS, from spreading around the world. He now heads WHO's global campaign to eradicate polio by the end of 2005. Once polio is eradicated, it will become only the second disease after smallpox to have been wiped off the face of the earth.

Dr. Heymann said most diseases cannot be eliminated. But polio is a good candidate because it does not exist in nature or in animals; it can only be transmitted from one human to another. Also, a good polio vaccine is available. "The oral polio vaccine is important for many reasons," explained Dr. Heymann. "Number one, because you do not require a needle and syringe to give it. You can give it orally. And this makes it possible to vaccinate large numbers of children in a very short period of time, which is very important when national immunization campaigns are conducted."

Hundreds of millions of children, even in war-ravaged countries, have been vaccinated against deadly and disabling diseases during national immunization days.

Aid agencies are expanding their vaccine coverage through so-called public-private partnerships, such as the Global Alliance for Vaccines and Immunization. The organization was launched in 2000 with a $750 million donation from the Bill and Melinda Gates Foundation.

Executive Secretary Tore Godal says the Alliance was created to reverse the decline in immunization coverage experienced by many developing countries in the 1990s.

"We have immunized over 30 million children with vaccines that were not available for them earlier, such as Hepatitis-B, Haemophilus influenza-B and yellow fever," said Mr. Godal. "We have expanded immunization coverage to reach out to an additional eight million children." The Alliance's aim, he added, is to prevent the deaths of three million children a year by improving the supply and distribution of existing vaccines and by developing new ones.

Research on vaccines against diseases such as diarrhea, pneumonia, HIV/AIDS and malaria is underway.

Such new vaccines will have the potential for saving millions of lives. But, aid agencies wonder whether money will be available to make them affordable for babies in developing countries.

This is part of VOA's series of reports on World Health