The World Health Organization told the maker of the anti-bird flu drug Tamiflu to ready its global stockpile for shipment, after the deadly virus passed among several Indonesians in the same family, officials said Saturday.

The U.N. health organization said it put Swiss pharmaceutical company Roche Holding AG on alert Monday for the first time, but its stockpile will remain in place.

"We have no intention of shipping that stockpile," WHO spokesman Dick Thompson told The Associated Press. "We see this as a practice run."

However, a separate WHO stockpile of 9,500 treatment doses was sent to Indonesia on Friday, along with protective gear.

"It's important to keep in mind that developing countries don't have their own stockpiles the way we do," Dr. Neil Rau, an infectious disease expert based in Canada, told CTV News. "Therefore it's important to provide that if needed."

Six family members have died from the H5N1 virus in the Sumatra village of Kubu Sembelang. It's the largest case of human-to-human transmission of bird flu yet, although doctors said the virus only passed among blood relatives.

"If this virus had evolved into a form that is more easily passed between people, you would have seen some other cases (outside the family) by now," WHO spokeswoman Maria Cheng told AP.

"The virus hasn't passed beyond the family."

The six dead in Kubu Sembelang is not the only case of the virus spreading among family members.

WHO has documented four or five other such clusters, where transmission also appears to have been limited to relatives.

Scientists theorize bird flu may be passed among humans through droplets coughed or sneezed into the air, which then contaminate surfaces or food.

Bird flu has infected at least 48 people in Indonesia and killed 36 -- almost as much as Vietnam's 42 deaths.

Indonesia does not contain outbreaks through the mass slaughter of poultry in affected areas; its government has said it would be unable to compensate farmers.

Roche will remain on alert for the next two weeks, double the incubation period of the last confirmed bird flu case.

Baschi Duerr, a spokesman for Roche, told AP the company's emergency stockpile consists of 3 million treatment courses.

"We are in very close contact with WHO, even today, and our readiness is geared to be able to deliver," he said.

More than 124 people have died from bird flu worldwide since 2003.

With files from The Associated Press