As researchers work to develop a vaccine to guard against pandemic bird flu, they are faced with both a scientific and logistical challenge: how to produce it in sufficient quantities to provide widespread protection.

Earlier this month, Anthony Fauci, director of the US National Institute of Allergy and Infectious Diseases unit, offered grounds for preliminary optimism when he announced successful results with a vaccine developed by Sanofi-Pasteur against the H5N1 flu strain.