Webster speculates that substandard vaccines may be preventing the expression of the disease in the birds but not stopping them from carrying or transmitting the virus through feces, or the virus from mutating [REF].
In order to protect their poultry from death from H5N1, China reportedly made a vaccine based on reverse genetics produced with H5N1 antigens, that Dr Wendy Barclay, a virologist at the University of Reading believes have generated up to six variations of H5N1 [REF].