U.S. officials on Wednesday defended a tactic used by the CIA to attempt to verify the whereabouts of Osama bin Laden — the covert creation of a vaccine program in Abbottabad, the town in Pakistan where he was later killed in a U.S. raid.

The vaccine drive was conducted shortly before the raid in early May on bin Laden’s compound, officials said, and was overseen by a Pakistani doctor who traveled to Abbottabad. The goal was to collect DNA evidence from residents to learn whether bin Laden lived in the compound.

A senior U.S. official said the campaign involved actual hepatitis vaccine and should not be construed as a “fake public health effort.”

“People need to put this into some perspective,” said the official, speaking on the 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 vaccine drive was first disclosed earlier this week by Britain’s Guardian newspaper.

The doctor who oversaw the effort has since been arrested by Pakistan’s Inter-Services Intelligence agency for cooperating with the CIA.

U.S. officials have said they are seeking to have him released, and 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 was due to arrive in Washington late Wednesday.

The senior U.S. official declined to say whether DNA from bin Laden’s relatives was collected as part of the vaccine program.

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 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 has long been an obstacle to the eradication of the polio.

Staff writer Greg Miller contributed to this report.