Asked by: Robert Leslie, Poole
Every January, government organisations and health researchers meet to decide which strains of influenza virus present the biggest threat for the following winter. The three or four worst strains are then injected into fertilised chickens’ eggs and incubated so that the virus will multiply.
After a few days the egg white protein containing virus particles is extracted and chemically inactivated, so it can’t cause flu itself. The vaccine is a dilute solution of this mixture, with some preservatives added.
Last year a new technique became available, which inserts DNA sequences into bacteria so that they will produce virus proteins. This has the same effect as stimulating your immune system but it’s much faster to manufacture.