U.S. officials ... 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 ... and was overseen by a Pakistani doctor who traveled to Abbottabad. A senior U.S. official said the campaign involved actual hepatitis vaccine and should not be construed as a fake public health effort. The vaccination campaign was part of the hunt for the world's top terrorist, and nothing else." 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. 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.