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THE LAST CASES: A child receives polio vaccine in Karachi, Pakistan, where misinformation and violence have complicated efforts to wipe out the disease.
FAREED KHAN/AP
THE INTERNATIONAL campaign to eradicate polio, which has vaccinated 2.5 billion people since it began in 1988—nearly all of them children—has faced one setback after another. Its goal of wiping out the disease from the planet, which was meant to happen in 2000, is about 16 years overdue—but getting close. The campaign has confined the disease to only three countries and hopes to reach its goal by the end of this decade.