KARACHI, Pakistan — Usman, who limps on a leg bowed by the polio he caught as a child, made sure that his first three children were protected from the disease, but he turned away vaccinators when his youngest was born.

He was furious that the Central Intelligence Agency, in its hunt for Osama bin Laden, had staged a fake vaccination campaign, and infuriated by American drone strikes, one of which, he said, had struck the son of a man he knew, blowing off his head. He had come to see the war on polio, the longest, most expensive disease eradication effort in history, as a Western plot.

In January, his 2-year-old son, Musharaf, became the first child worldwide to be crippled by polio this year.

“I know now I made a mistake,” said Usman, 32, who, like many in his Pashtun tribe, uses only one name. “But you Americans have caused pain in my community. Americans pay for the polio campaign, and that’s good. But you abused a humanitarian mission for a military purpose.”