Governments bracing for a second, possibly more lethal, wave of swine flu are all grappling with the same unforgiving dilemma: with not enough vaccine to go around, who is going to get jabbed first?

Any lingering hopes that pharmaceutical companies could rapidly fill orders for more than a billion doses from northern hemisphere countries alone were quashed this week by the World Health Organisation (WHO).

"We need to gather advice on priority groups for initial protection," WHO head Margaret Chan said Friday.

"This is one of the most difficult decisions governments around the world will need to make, especially as we know that supplies will be extremely limited for some months to come."

But national leaders looking for guidance from international health authorities on how to best distribute vaccines that will not be available in most cases before early October, at best, are bound to be disappointed.

The European Union has yet to issue any guidelines specific to the new strain of A(H1N1) influenza that has swept across the globe, infecting hundreds of thousands and claiming at least 1,800 lives.

The WHO does suggest that health care workers should be given priority, a policy embraced by most states, but stops short of making further recommendations.

"Individual countries have to look at their own conditions and adapt," WHO spokesman Melinda Henry told AFP from Geneva.

"They have to decide whether they want to stop transmission, protect essential infrastructure, or reduce illness and death."