The government is starting work on a second vaccine to battle bird flu.
Health and Human Services Secretary Mike Leavitt (LEH'-vit) says government scientists have been told to develop a second vaccine, to add to several (m) million doses of a first bird flu inoculation already in the government stockpile.
That vaccine was based on a sample of virus taken from Vietnam in 2004. Health officials think the virus has mutated since then, so the potentially deadly strain now popping up in Africa and Europe may be different.
The World Health Organization calls bird flu a greater global challenge than any previous infectious disease.