Jakarta, Indonesia ? The World Health Organization has detailed the first evidence that a person likely caught the bird flu virus from a human, then passed a slightly mutated version to another person. But experts said Friday the genetic change did not increase the threat of a pandemic.

The investigation said the mutation of the H5N1 strain of the virus occurred in a 10-year-old Indonesian boy who was part of the largest cluster ever reported. The index case is believed to have been infected by poultry. She then likely passed it to the boy and five other blood relatives. The boy is then thought to have infected his father, whose samples showed the same mutation, according to the report obtained by The Associated Press.

Only one infected family member survived.

“It stopped. It was dead end at that point,” said Tim Uyeki, an epidemiologist from the U.S. Centers for Disease Control and Prevention.

Uyeki, who was part of the investigating team, stressed that viruses are always changing slightly, and there was no reason for this mutation to raise alarm because the virus has not developed the ability to spread easily among people.

U.N. bird flu chief David Nabarro said the findings nevertheless emphasized the importance of continuous monitoring of the H5N1 virus in both humans and poultry.

“We were fortunate in that the change that took place did not result in sustained human-to-human transmission,” he said Friday. “This is a vivid reminder of the need to keep a very close watch on what the virus is doing.”

Experts fear the H5N1 virus eventually could mutate into a highly contagious form that spreads easily among people, potentially sparking a global pandemic. The current virus remains hard for people to catch, and most human cases have been traced to contact with sick birds.

The WHO report was distributed during a three-day meeting in Jakarta attended by some of the world’s top bird flu experts. Indonesian officials called the closed-door session to ask for help in coping with the virus, which has infected more people in Indonesia this year than anywhere else – killing an average of one person every 2 1/2 days last month.