Editor’s note: The following is the introduction to a special e-publication called Polio: Pushed to the Brink (click the link to see a table of contents). Published this summer, the collection draws articles from the archives of Scientific American.

When I began my career in public health in the 1960s, poliomyelitis was one of the most feared diseases in the world. Even just 25 years ago the virus infected more than 350,000 people, causing paralysis and irreversible disfigurement.

Thanks to vaccines and a tremendous international effort, today that number is down to just a few hundred cases globally. Still, for every person who shows the characteristic signs and symptoms of polio, 100 or more individuals carry the virus and can spread the disease without their knowledge. And the areas where polio remains are among the most remote and unstable corners of the planet. The road before us isn’t easy, but we cannot rest until polio is truly and completely wiped out for good.

Winning the Fight in the Americas
In the early 1980s, when polio continued to be widespread in the Americas, there were those who said eradication could not be done, that the obstacles were insurmountable. Nevertheless, on May 14, 1985, the Pan American Health Organization (PAHO) announced its audacious goal to eradicate the disease in the region by 1990.

Among our many obstacles, civil unrest threatened to undermine our efforts to stop the spread of polio in Central America, Peru and elsewhere. Some health workers feared for their lives where warring factions threatened their safety. But polio doesn’t balk in the face of armed conflict. It isn’t hindered by the same logistical challenges that deter vaccinators from reaching children where roads stop and transport becomes next to impossible.

To beat polio in the Americas, we had to ensure that all children, even the hardest to reach, received polio vaccines—not just once, but several times—until the threat of polio had passed. For example, in El Salvador, we called on UNICEF, the Red Cross and even the Catholic Church to intervene so we could gain political (and rebel) support, which was absolutely necessary if we were to succeed. After many months of deliberations between government and guerilla forces, we successfully negotiated a cease-fire. During these brief “days of tranquility,” warring parties laid down their arms so that health workers could safely and effectively carry out nationwide immunization campaigns. Eventually three days of tranquility were held every year from 1985 to 1991, and they served as a bridge for peace in the region. Practically every child in El Salvador was vaccinated each year, until peace was achieved in the early 1990s.

The situation in Peru was more complicated, and negotiating a cease-fire with the ruthless Shining Path guerrilla movement proved unsuccessful. But we would not let this setback stop us from reaching our eradication goal. We organized a series of mop-up campaigns—door-todoor immunizations in specific focal areas—to help limit polio to just a few areas. We used the media and other public events to appeal to everyone—including the guerrillas—to cooperate with these vaccination efforts. I would like to note that when key guerrilla leaders were captured by government forces, several of those individuals were recognized as having directly assisted the vaccination campaigns.

It was in Peru that the last case of polio was reported in the Western Hemisphere, in 1991. The World Health Organization (WHO) declared the Americas polio-free in 1994.

Global Polio Eradication
Country by country, polio is being eliminated, often amid intense political turmoil. The Democratic Republic of Congo adopted the “days of tranquility” method to vaccinate more than four million children, and within 18 months of the start of the campaign, transmission of polio was successfully halted. Once thought to be the greatest challenge to global polio eradication, India has not reported a single case of polio in more than two years. These successes give me hope.

Today endemic polio remains in only three countries: Nigeria, Pakistan and Afghanistan. Other countries have reported imported cases, showing how easily polio can spread if left unchecked. The final obstacles to global polio eradication may be the toughest we have ever faced. On Friday, February 8, 2013, armed gunmen attacked a vaccine clinic in northern Nigeria. Nine health workers were reportedly killed in this incident, and others were injured. In recent months various coordinated attacks have occurred in Pakistan, which have left at least 16 health workers dead.

Yet I know that the global health community and all of those who continue to combat this disease—from the WHO to local health workers— will not falter and will not give up their efforts to eradicate polio. The legacies of Albert B. Sabin and Jonas E. Salk teach us that success will rely on worldwide collaboration and some unlikely allies.

Throughout this issue, you will learn about the trials and triumphs that have led us to where we stand today. We are on the brink of global polio eradication, and I am confident we will see this disease wiped off the planet by the end of this decade. We cannot let polio beat us, not when we are on the verge of eradicating a disease for only the second time in human history.