Recent worldwide progress toward wiping out polio is the latest indication that significant improvements in global health are possible when governments, institutions, and individuals work together to address common concerns at the national and international levels. But with polio eradication near, the UN's World Health Organization (WHO) and its partners in this global effort are increasingly worried that support for the project may wane before the final hurdles are overcome.

The near-eradication of polio puts the United Nations (UN) on the brink of its greatest health achievement since it led the push to eradicate smallpox in the early 1970s. Preliminary data obtained from the WHO indicate that the number of new polio cases reported worldwide dropped to just over 3,200 in 1998 -- the lowest case-count on record. Reported polio cases have declined by 90 percent in the past decade, since WHO launched its 1988 global vaccination campaign to eradicate poliovirus by the year 2000. (See graph and table).

For much of this century, and particularly prior to discovery of the polio vaccine in the 1950s, poliomyelitis was one of the most deadly and crippling diseases of our time. Still today some 10-20 million people worldwide -- including many children in the developing world -- remain paralyzed from the virus, unable to walk without the help of leg braces or breathe without devices such as the "iron lung." The actual number of polio cases worldwide, thought to be about 10 times the figure reported, is now estimated at only 30-35,000.

The steady disappearance of polio is the result of social and political commitment by national governments and the international community. By late 1998, 118 countries had conducted at least one round of National Immunization Days (NIDs), during which all children under five were administered two doses of Oral Polio Vaccine (OPV) one month apart -- compared with only 21 countries a decade earlier. In 1997, 450 million children -- about two-thirds of the world's under-five population -- were immunized during large campaigns in 80 countries.

Polio is one of few diseases that can be wiped out because the virus is transmitted only through person-to-person contact and cannot persist in the environment for long periods of time without a human host. The only other disease that has ever been eradicated is smallpox, which was wiped out in 1977.

The eradication of polio is also possible because the oral vaccine against the disease is highly effective and cheap (about $1 per dose, or $3 per child), and usually provides lifelong immunity to the virus. Widespread use of this vaccine has eliminated polio from vast regions of the world where it was once pervasive. Ten years ago poliovirus circulated freely on all continents except Australia, but in 1998 a record 188 countries reported zero polio cases -- double the number of a decade earlier.

The only WHO region with official "polio-free" status is the Americas, where the last case of polio was recorded in Peru in 1991. The Western Pacific, Eastern and Western Europe, and parts of Northern and Southern Africa are also now considered polio-free following eradication efforts, but will not receive official certification until they have met the WHO requirement of reporting three consecutive years of zero polio cases.

Despite the overall decline worldwide, 27 countries were still reporting polio transmission as of late 1998. The principal remaining reservoirs of the disease are South Asia, particularly India, Pakistan, and Afghanistan; and Western and Central Africa, particularly Nigeria and the Democratic Republic of Congo. The virus also persists in Turkey and in Kurdish-occupied areas of Iraq, where international health workers have had difficulty obtaining government cooperation and permission to reach and vaccinate children.

Among the greatest obstacles to eradication are the lack of basic health infrastructure for vaccine distribution and the crippling effects of civil war. In polio endemic countries such as Angola, Somalia, and Sierra Leone, internal conflict has meant the suspension of immunization programs, severance of vaccine supply lines, and destruction of health services. For instance, in August 1998 the Democratic Republic of Congo -- a country that four years ago witnessed one of the largest polio epidemics of the century -- was forced to postpone its scheduled National Immunization Day and later suspend its vaccination program after health care workers fled hospitals devastated during the ongoing war.

On a more positive note, in some war-torn countries -- including Sudan and Sri Lanka -- immunization efforts have actually led to momentary cease-fires, as combatants laid down their weapons to allow health workers to reach and vaccinate young children.

Another challenge faced by the global polio eradication effort is maintaining the 2-8 degrees Centigrade temperatures required to keep live vaccines potent in extremely hot or remote areas. The recent introduction of color-coded, heat-sensitive "vaccine vial monitors" has made it easier for health care workers to recognize whether vaccines have suffered excessive heat exposure. However, the effectiveness of the monitors hinges on awareness of proper vial distribution and use.

As the target year for polio eradication nears, WHO and its partners in the global effort -- including UNICEF, Rotary International, vaccine manufacturers, and the governments of the United States, United Kingdom, Australia, Canada, Denmark, Japan, and Germany -- are increasingly worried that support for the project may wane before the most difficult hurdles are overcome. For instance, funds are still lacking for the initiative's challenging final phase -- door-to-door "mopping-up" campaigns to immunize children in densely populated, high-risk districts. Although 50-80 percent of the costs are covered by the endemic countries themselves, WHO estimates that an extra $350 million in additional international support will be needed before 2001.

If all goes well, the final case of poliovirus outside the laboratory setting will probably be identified in 2000 or 2001, and the world will achieve official "polio-free" status at the earliest by 2005. Global child immunization will then continue for an additional five-year period to ensure that the disease has really been wiped out from all regions. From that point on, countries will begin to realize the tremendous benefits from no longer having to immunize infants or to treat or rehabilitate people affected by polio-saving an estimated $1.5 billion per year. Western Europe alone will save about $200 million annually, and the United States will save about $230 million-twice as much as it will need to spend per year on global polio eradication in the near future.

In addition to financial savings, successful polio eradication will leave behind a legacy of effective international health cooperation, as well as a global disease prevention network that can be used to combat a range of other childhood killers-including tuberculosis, whooping cough, and diphtheria. Already, WHO is weighing the possibility of selecting two additional viral diseases, measles and rubella, as eradication targets in the next 10-15 years.