Vaccinations have become so commonplace that they now are considered a rite of passage--something kids get at certain ages or something travelers obtain before they leave home. While vaccines have been around for hundreds of years, much of their impact has occurred just within the last few decades. And they hold promise to revolutionize public health in the next century.

Smallpox already has been eradicated, and other diseases, such as polio, measles, chicken pox, and mumps, are on the way to becoming extinct, even in the poorest countries. For all this we first can thank a few cows.

The exact birth of vaccines is questionable. Some date their use back to the 7th century, when Indian Buddhists drank snake venom to build up immunity against bites. The first written record for the treatment of smallpox appears in the 9th century in China. But credit for today's vaccines goes to Edward Jenner, a country doctor in England who in the late 1700s saw the link between cowpox and smallpox.

The story has it that a milkmaid told Jenner that she and the others who milked cows suffering from cowpox were not susceptible to smallpox. Intrigued, Jenner in 1796 infected a boy with cowpox and subsequently injected him with pus from a smallpox lesion, a move today that most likely would have put him before a medical review board. As he suspected, the boy did not get smallpox. Jenner's procedure came to be known as vaccination, taken from the Latin word for cow, vacca.

Almost a century later there were vaccines for rabies, typhoid, cholera, and plague. In the early 20th century, that list grew to include tuberculosis, yellow fever, whooping cough, influenza, diphtheria, and tetanus. And still later there were vaccines for polio, measles, mumps, chicken pox, rubella, typhoid, Japanese encephalitis, hepatitis, pneumococcus, meningococcus, hepatitis B, tick-borne encephalitis, and typhoid (Vi). Among the newest vaccines are the Hemophilus Influenza Type B (HiB) and the recently U.S.-approved rotovirus vaccine against deadly childhood diarrhea.

Global eradication of smallpox was no easy feat. The World Health Organization (WHO) started the debate in the 1950s. But it wasn't until the 1960s that organized campaigns took off. While effective and cost-efficient, vaccination programs are labor-intensive. Then, like today, vaccines have to be administered. It is a one-on-one job, not a prescription that can be filled by a local pharmacy. Supported by a worldwide effort and the conviction to eradicate smallpox, brave cadres of usually young and dedicated doctors went from door to door and village to village to vaccinate children and adults. In 1971, their job was completed in the Western Hemisphere. And six years later the entire world was free of smallpox.

Polio: The Next Hurdle

Polio was among the scariest of diseases in the 20th century, mainly because it so often struck young children and left them crippled for life. The disease evokes images of iron lungs and polio wards. In the mid-1950s Dr. Jonas Salk developed the first polio vaccine. Six years later Dr. Albert Sabin developed an oral polio vaccine.

In 1985, Dr. Carlyle Guerra de Macedo, then-Director of the Pan American Health Organization (PAHO), proposed the goal of eradicating polio from the Western Hemisphere, and the ministers of health of the countries of the Americas accepted the challenge. Many of the same public health pioneers who had taken part in the smallpox eradication campaigns were pressed into action once again. Dr. Ciro A. de Quadros, who today is Director of PAHO's Special Vaccine Initiative, recalls that local teams throughout the Americas set out to vaccinate every potentially susceptible child against the dreaded disease.

In addition to braving isolated and rugged terrains, health workers had to ensure that the vaccines were kept at a cool temperature, which frequently meant hauling ice chests through the jungles. The polio campaign is replete with heroes and stands as a model of dynamic international cooperation, with assistance coming from Rotary International, the U.S. Agency for International Development (USAID), UNICEF, the Inter-American Development Bank, and the Canadian International Development Agency (CIDA).

Success was attributed to national immunization days, follow-up campaigns, surveillance, rapid investigation, aggressive outbreak control, and community monitoring. The last known case of polio in the Western Hemisphere struck 2-year-old Luis Fermín Tenorio Cortez in rural Peru in 1991. In September 1994, before a packed audience at PAHO's Washington, D.C., Headquarters, Nobel Prize winner Dr. Frederick Robbins announced the eradication of polio from the Americas.

"It was fantastic," recollects de Quadros, who fought against smallpox in Africa and polio in the Americas. "There were tears; there was an outbreak of cheers and applause. We made it happen and saw an unbelievable accomplishment."

Now WHO is attempting to eradicate polio globally. When that work is completed, the world will save US$ 1.5 billion each year.

Only a Childhood Disease

Just a few decades back, measles, mumps, chicken pox, and rubella, known as German measles, were considered minor annoyances, something all children went through. Yet, according to PAHO, some 135 million measles cases killed up to 8 million children worldwide annually before a vaccine became available in the 1960s. And even with a vaccine, measles continues to be the leading killer among childhood vaccine-preventable diseases. "Measles is Highly Dangerous," the PAHO Web page cautions visitors.

Again, seeking joint action, the countries of the Americas united in 1994 to call for an end to measles by the year 2000. Returning to many of the time-tested measures and with effective surveillance systems already in place, national health authorities redoubled their efforts to achieve high coverage rates during specially-convoked immunization days. The measles initiative is receiving the support of USAID, the Governments of Spain and the Netherlands, and CIDA.

The Caribbean nations already had a head start. A few years earlier, they had launched a massive "Make Measles History" campaign whose popular appeal stimulated tremendous response. The English-speaking Caribbean went for more than five years without a single case of measles.

But the disease has been a cagey enemy to conquer. Some 13.6 million children under 5 years old in 11 countries have not had the needed follow-up vaccinations. And national immunization programs have had trouble identifying pockets of unvaccinated children. In 1998, measles outbreaks occurred in Brazil, Bolivia, and Argentina. Health officials intensified their vaccination campaigns.

De Quadros says health officials had estimated it would cost US$ 53 million to eradicate measles in five years but that only US$ 20 million have become available so far. "We have a tremendous handicap until all the resources are there," he says, adding that measles, like so many other diseases, strikes hardest at the poor. "Measles doesn't kill nourished children, but it kills 1 to 2 million children each year in the developing world."

A Mild Rash

In the English-speaking Caribbean, where the measles campaign showed impressive results, health officials have embarked on an effort to stop rubella by the year 2000. The rubella virus, according to PAHO, was first detected in the mid-1800s. Even more than measles, rubella was considered just a minor nuisance. Then came the 1963-1965 epidemic, principally affecting the United States.

"The epidemic peaked in 1964," says Dr. Stephen Epstein, Associate Clinical Professor of Otolaryngology at the George Washington University School of Medicine in Washington, D.C. "In 1968, we began seeing 3-year-olds who were not hearing. We learned then that rubella was not a problem for the children, but for the mothers."

Rubella, in and of itself, still was just a childhood disease. It did, however, present a crisis situation for pregnant women during their first trimester. Expectant mothers who contracted rubella during this fragile period all too often gave birth to children with severe defects, such as blindness, deafness, cardiovascular problems, and mental retardation. Between 1964 and 1965 in the United States, there were about 11,000 fetal deaths or induced terminations of pregnancy and 20,000 infants born with the defects, known as congenital rubella syndrome, according to a paper prepared by Drs. Alan R. Hinman, Bradley S. Hersh, and Ciro A. de Quadros.

"We began to look at an approach for managing these children," recalls Epstein, who was born with a hearing deficiency. "We put together groups of physicians, audiologists, psychologists, speech and language pathologists, social workers, and educators. Parents were devastated. Being hearing impaired, I felt I understood what parents go through, what the kids go through."

Dr. Merceline Dahl-Regis, Chief Medical Officer of the Bahamas, adds that the price tag for caring for children with congenital rubella syndrome is very costly. It was for that reason the English-speaking Caribbean set out to eliminate the disease.

"We decided to do a mass campaign, and we struggled to figure out who we should vaccinate, and how to do it," Dr. Dahl-Regis explains. "We went to the schools, the postpartum clinics, work sites." She said the public response was particularly encouraging, with corporate groups calling to make arrangements for workplace immunizations.

De Quadros, who led the PAHO effort to work with Dr. Dahl-Regis, explains that rubella caused 20,000 cases of children born with defects in Latin America. He adds that nations often have competing political and economic priorities and urges them to follow through on their commitment to rid the Hemisphere of measles.

According to U.S. statistics, every dollar spent on vaccines in the United States translates into a savings of about $7 in health care costs and lost work time. The global smallpox eradication program cost US$ 298 million, but the savings over time are put at US$ 1.5 billion.

Meanwhile, scientists continue working to develop new vaccines, easier ways to deliver them, and measures to keep the research affordable. Before the HiB vaccine, according to de Quadros, there were about 20,000 infections annually in the United States with up to 1,000 deaths. The HiB infection often led to meningitis, a serious infection of the fluid and lining that cover the brain and spinal cord.

The rotavirus vaccine will protect children from a severe form of diarrhea that infects 3.5 million in the United States alone and kills up to 1 million worldwide each year, according to the vaccine's manufacturer, Wyeth-Ayerst. Other researchers in the United States came up with a potato genetically engineered with a vaccine to prevent diarrheal disease.

Brazilian-born de Quadros is a model of enthusiasm and a staunch believer in vaccines. "The future of public health is in vaccines," he says. "That's the only instrument that is really preventive, easy to administer, and relatively cheap. Vaccines are the most cost effective tool known in medicine.

"We're going to reach a level where we will have vaccines for chronic diseases," he adds. "The 21st century will be the century of vaccines the way the 20th century was for antibiotics. I have no doubt about it."

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Bryna Brennan is Chief of PAHO's Office of Public Information.