Microsoft founder Bill Gates said the battle to eradicate polio was one of the toughest the world has faced, but said it could be conquered by 2018.
Delivering the annual Richard Dimbleby lecture in London on Tuesday, Gates, the United States' richest man, said ridding the world of polio would be "one of the great moral and practical achievements of our age".
The 57-year-old businessman turned philanthropist, who is putting his resources into the fight, said that though polio was still endemic in Afghanistan, Pakistan and Nigeria, vaccination campaigns could eliminate it within six years.
"We are working to wipe the virus off the face of the earth, and we have almost succeeded: There are only three countries in the world where the virus is still being transmitted. Fewer than 250 children were paralysed last year," he said.
"Stopping these last cases of polio in these last countries, however, is among the most difficult tasks the world has ever assigned itself.
"The fight to eradicate polio is a proving ground, a test. Its outcome will reveal what human beings are capable of, and suggest how ambitious we can be about our future."
Polio -- which afflicts mainly the under-fives causing death, paralysis and crippled limbs -- travels easily across borders and is transmitted via the fecal matter of victims.
Though vaccines are relatively cheap and easy to deliver, said Gates, it is "stunning to me" that millions of children do not get them.
"The last mile is not only the hardest mile; it's also much harder than I expected," he said.
However, "I see strong commitment from leaders in all three endemic countries," he added.
"Polio doesn't kill as many people as AIDS, tuberculosis, malaria, or rotavirus. It's not even close. So why should the world focus on eradicating it?
"When polio is gone, we can use the same systems, technology, and people to deliver other lifesaving solutions, especially routine vaccinations for diseases like diarrhea, measles, and pneumonia," he argued.
"The global polio community has a detailed plan for getting from here to eradication.
"This plan says that if the world supplies the necessary funds, political commitment, and resolve, we will certify the eradication of polio by 2018.
"If the world delivers, then we will eradicate polio within six years.
"We should see it as one of the great moral and practical achievements of our age."
Gates' predecessors in giving the lecture include former US president Bill Clinton and Prince Charles, the heir to the British throne.
[Image via Agence France-Presse]