"The pandemic influenza clock is ticking. We just don't know what time it is," says Ed Marcuse, a member of one of the two federal vaccine advisory groups that put the final touches on the Department of Health and Human Services' draft Pandemic Influenza Preparedness and Response Plan.

During an all-day meeting in Rockville, Md., yesterday, the advisers voted unanimously on a scheme for rationing emergency pandemic flu vaccine and recommended that the federal government buy up to 600 million doses—enough for the entire country.

The plan responds to the deadly strain of bird flu called H5N1 still devastating chickens and other poultry throughout Asia. This new virus has now moved into wild migratory birds, tigers, and cats. And, according to the World Health Organization, it has killed 54 of the 108 people who contracted it, mostly from their direct contact with sick birds. Experts fear the strain is threatening to morph into a fast-spreading form that is easily transmissible from human to human—the key ingredient that could trigger a global influenza epidemic of the kind that killed tens of millions of people worldwide in 1918.

With current technology, it will take well over a year to produce enough vaccine for the entire population. Since it's a new strain, each person will need two immunizations, not the usual one. That means the early months of an epidemic will call for major rationing. The plan lays out just who will get the vaccine, in descending order of priority:

• Group 1. The highest-priority group includes 9 million healthcare workers involved in direct patient care; 40,000 people who are making the vaccine and antiflu medicines; and some 37 million people who are at greatest risk if they get the flu, namely those over age 64 with a medical illness, younger people with two serious underlying medical conditions, pregnant women, and all household contacts of children under 6 months of age. Also in this top group are key government officials and specialized pandemic flu responders.
• Group 2. In the next tier are healthy seniors; younger people with one risky health condition; young children between 6 to 23 months old (the vaccine is not recommended for infants under 6 months); and workers in critical fields like public safety, utilities, emergency response, transportation, and telecommunication. This group is 68 million strong.
• Group 3. The third priority is 500,000 people, including key government healthcare decision makers and those working in mortuary services.
• Group 4.At the bottom are the remaining 179 million healthy people, 2 to 64 years old, not included in any other category.

The working group did not include nursing home residents, who typically get annual flu shots, among the highest-priority group. Instead, they advise vaccination of the nursing home healthcare workers and the prophylactic use of the antiviral drug oseltamavir (Tamiflu) in the advent of an outbreak.

The advisory committee acknowledged that the prioritization could change quickly once an outbreak occurs. For example, in the pandemic of 1918 nearly half of those who died were young healthy adults. And in Asia, most of the deaths from H5N1 bird flu have been in younger people.

Tamiflu is the best bet for treating those who catch the deadly virus. HHS has already stockpiled 2.3 million treatment courses. But since an outbreak is estimated to have an attack rate of 25 percent, the advisory group proposed that the Tamiflu stockpile be increased to a whopping 133 million courses. A typical 5-day course of the drug cost about $50 wholesale, but that may be lower if it's sold in bulk.

And who will pay for all this? Because it would be a serious national emergency, the working group says the government should. Only federal pockets are deep enough to guarantee the massive orders ahead of time so manufacturers can build up capacity to make the huge volumes.

But the advisers were also convinced that government purchase of all pandemic vaccine available in this country would bring added benefit: HHS would then have the power to enforce its rationing priorities, assure the drugs are fairly distributed, and fend off the chaos that hit last fall when an unexpected manufacturing plant shut-down led to shortage of the annual flu-shot supply.

The draft pandemic plan, which has been under review since it was released for public comment on Aug. 26, 2004, will be finalized and sent to HHS Secretary Michael Leavitt in August.