Gregory Hartl, a spokesman for the Geneva-based UN health agency, says the 49-year-old Briton was traveling to Melbourne, Australia, to attend the 20th International AIDS conference, which starts Sunday.
Hartl told reporters today in Geneva that Thomas, who regularly briefed journalists and responded to media requests for interviews and comment, had been with WHO for more than a decade.
He said Thomas "will be remembered for his ready laugh and his passion for public health."
Hartl says no other UN employees were aboard the plane, which was flying from Amsterdam to Kuala Lumpur, Malaysia, and crashed Thursday with 298 people on board.