Kieny said WHO would also work to get better viruses for companies from which to make vaccines. She said the strains that had been distributed did not grow very well in chicken eggs - used to make all flu vaccines.

One exception - AstraZeneca's MedImmune unit makes a live virus vaccine that is squirted up the nose and it is easier to produce, Kieny said.

WHO said countries should continue with their normal vaccination programs against seasonal flu. Kieny said the seasonal H3N2 strain was also very active now in the southern hemisphere's winter.

Sanofi-Aventis, Novartis, Baxter, Schering-Plough's Nobilon, GlaxoSmithKline, Solvay, CSL and AstraZeneca's MedImmune are among those working on flu vaccines.