The Guardian newspaper disclosed the existence of the CIA vaccine drive earlier this week, saying that the agency had recruited a senior Pakistani doctor to travel to Abbottabad to organize it.

That doctor has since been arrested by the country’s Inter-Services Intelligence agency for cooperating with the agency, and U.S. officials have said they are seeking to have him released. The issue could come up at talks between the CIA’s acting director, Michael Morell, and his Pakistani counterpart, Lt. Gen. Ahmed Shuja Pasha, who is due to arrive in Washington today.

A senior U.S. official said the vaccine campaign was conducted by medical professionals and should not be construed as a “fake public health effort.”

“People need to put this into some perspective,” said the official, speaking on condition of anonymity because of the sensitivity of the issue. “The vaccination campaign was part of the hunt for the world’s top terrorist, and nothing else.  If the United States hadn’t shown this kind of creativity, people would be scratching their heads asking why it hadn’t used all tools at its disposal to find bin Laden.”

The campaign was conducted shortly before the May 1 raid on bin Laden’s compound. The official declined to say whether DNA from bin Laden’s relatives was collected.

Officials have previously said, however, that they used DNA analysis to confirm bin Laden’s identify after he was killed. In doing so, they used samples taken from known relatives.

The tests concluded with near-perfect certainty that the man killed at the Pakistani compound was the al-Qaeda leader. The chance of a false positive from the DNA testing, an intelligence official said, was “approximately one in 11.8 quadrillion.”

The Associated Press, meanwhile, has reported from Islamabad that Pakistani officials and international health organizations are concerned that the CIA-organized effort could harm immunization programs in the country, where public skepticism of vaccinations have long been an obstacle to eradication of the polio.