# 3271
The H5N1 `bird flu’ virus now comes in a number of very different strains, with as many as 10 distinct clades having been identified around the world.
Over time, influenza viruses mutate, or pick up genetic material from hosts, and drift away from the genetic profile of their ancestors.
That means that vaccines based on earlier clades of the virus are likely to be less effective over time.
Accordingly, CDC and the WHO must occasionally select a strain of the H5N1 virus to produce a new `seed strain’ for use in the manufacturing of a pre-pandemic vaccine.
While in the past virus samples from South East Asia have been used to create these `seed stocks’, the recent spike in human cases in Egypt (along with a much lower mortality rate) has captured the attention of world health authorities.
A new seed strain based on one of the currently circulating Egyptian strains is now available for manufacturers who wish to use it to produce a pre-pandemic vaccine.
Scientists develop basis for bird flu vaccine
Thu May 28, 2009 1:33pm BST
GENEVA (Reuters) - Scientists have used bird flu virus samples from Egypt to develop a new basis for a vaccine against the toxic H5N1 strain that continues to circulate, the World Health Organisation said Thursday.
Avian influenza kills about half the people it infects, but unlike the quickly circulating H1N1 flu virus has not been shown to pass easily between humans to date.
In a statement, the WHO said the seed virus was developed at the U.S. Centres for Disease Control and Prevention in Atlanta "thanks to the ministry of health and population of Egypt for providing virus specimens."
