According to Seymour Hersh the fake vaccination work wasn't even to find Bin Laden, but to cover the actual CIA asset

Hersh writes that while Afridi was indeed a CIA asset, collecting information on militants, the fake vaccination campaign was invented as a cover story for a Pakistani military doctor who had been treating bin Laden for years, and who actually obtained DNA for the Americans.

(Later got locked up by Pakistan, never trust the Americans lesson #286)