In pursuit of a universal flu vaccine

Developing a universal flu vaccine that would protect against all seasonal and pandemic strains of the virus is no easy task, and new research suggests that one of the most promising strategies -- creating a vaccine that targets the 'stalk' of a protein that covers the flu virus -- is a strong one, but isn't completely bulletproof. Researchers found that the stalk of the hemagglutinin protein can vary in response to pressure from the immune system.