Why Can't the World Eradicate Polio?

In the universe of global diseases, polio would seem to be a minor problem. Fewer than 2,000 people in the world were stricken last year. AIDS and malaria, by contrast, killed more than three million people. In a list of the world's most threatening infectious diseases, polio would rank pretty far down—past measles, meningitis, influenza and drug-resistant tuberculosis, to name a few. Which raises the question: why did Bill Gates release $255 million of his foundation's money on Wednesday to fight polio?

The answer many health officials give is that polio is on the brink of being eliminated once and for all. A campaign of mass inoculations around the world, led by the World Health Organization, has reduced cases by 99 percent, cornering the disease in a few pockets of resistance. What's needed, health officials argue, is an infusion of funds to get them over the hump.

Trouble is, it's not clear that more money is going to do the trick. It's not easy to wipe a disease off the face of the planet—especially one like polio, which spreads easily and quickly through contact and occasionally through contaminated food and water. Only one in 200 children who contract the virus shows symptoms (usually paralysis), which makes the other 199 silent carriers. Indeed, more than two decades of fighting the disease around the globe has taught health workers that it is far more stubborn than originally thought. The failure to deliver the knockout blow has cast doubt on whether eradication is a viable strategy in the war on polio—even with a donor as bold and wealthy as Gates.

The polio eradication campaign began in earnest in 1988. It came on the heels of the smallpox campaign, which became the first (and only) disease ever to be eradicated; the WHO had declared it dead eight years before. Even though polio cases numbered 350,000 that year, it was by no means the most urgent threat, but health officials decided that a campaign to deliver the vaccine would serve also to improve access to vaccines for measles and other diseases. That turned out to be true for the most of the world. Polio dropped to a little more than 1,600 cases last year, but it hasn't disappeared. It stubbornly persists in several poor, densely populated areas—for reasons that money may not fix.

The most difficult challenge is Nigeria, where the culprit is poor governance. Despite the cooperation of the health ministry in Abuja, polio vaccines aren't being delivered reliably to children in Kano, a northern state where 20 to 30 percent of children remain unvaccinated. One problem is that the oral vaccine, which is cheaper than the injectable one, requires refrigeration, which is hard to come by in Africa. Also in Nigeria's north, illiteracy and a lack of trust in the government, which is notorious for corruption, may be the bigger problem. In 2003, inoculations in Kano came to a halt when rumors spread among tribespeople that the vaccine caused sterility. By the time health officials were able to convince local leaders that the rumors were unfounded, the virus had "exploded" out of Nigeria, says Dr. Steve Cochi, a senior advisor at the Centers for Disease Control in Atlanta. It quickly spread to 20 or so neighboring sub-African countries where it had previously been eliminated as well as to Yemen and distant Indonesia. Putting out that fire set the eradication effort back several years and added nearly $1 billion to its cost. More resources would help health workers respond to such a setback in the future, but getting more children to take the vaccines is going to take some doing.

The problems in northern India are completely different, but no less intractable. Although local government in Uttar Pradesh and Bihar have been efficient and cooperative in carrying out inoculation, the vaccines themselves are not wholly effective. Scientists don't understand exactly why, but they suspect that the typical child harbors so many intestinal bugs that the immune system is overwhelmed and fails to pick up on the vaccine. In relatively sanitary Europe or the United States, a child typically requires three doses of an oral vaccine to gain immunity; kids in northern India need as many as 12 doses. Getting this medicine to children and keeping track of who's gotten what is a staggering logistical challenge.

New funding would help, of course. All told, contributions from Gates, the Rotary Foundation and the German and British governments amount to an infusion of $630 million toward the effort. That could help bring injectable vaccines, which are more effective and expensive than the oral versions, to India. It could also help increase the support for inoculations in Nigeria, reaching more children, and increasing the presence of health workers to advocate for the program. On the other hand, it won't guarantee that health workers will reach every last child. Nor will it do much to help efforts in war-torn areas of Pakistan and Afghanistan, where the disease also persists. "New funding is necessary but not sufficient," says Cochi. "The job will be won or lost based on what happens in the countries and at local levels."

Smallpox took about a decade to wipe out. The polio effort, now 21, is burning through more than $600 million a year, with no end in sight. D.A. Henderson, the former WHO official who headed up the smallpox program in the 1970s, believes that control, rather than eradication, might be the best option for polio—dialing back inoculations, and concentrating on responding quickly to outbreaks. Cochi agrees that the current program is unsustainable but fears that a cutback in inoculations would lead to an unacceptable rise in new cases. Eradication is an all-or-nothing gamble: the disease is wiped out, or it comes back. Gates and the other donors are upping the ante.