H1N1: Vaccine Production Delayed

Flu viruses contain eight genetic elements. Vaccine strains contain two genes for the main surface proteins of the virus the vaccine is aimed at, plus six from a strain that grows well in chicken eggs, which is where most flu vaccines are produced.

These vaccine strains are produced either by reverse genetics, in which the eight genetic elements are artificially combined using genetic technology; or by allowing the two viruses to mix naturally. WHO collaborating labs used both methods to produce seed strains for the pandemic virus to make sure there were no unforeseen problems with one or the other.

Yet both methods have performed equally badly, each producing one of the two fastest-growing strains. The other strains are presumably growing even more slowly.

Vaccine companies are trying to tweak the vaccine strains to select faster growing ones, while WHO collaborating laboratories are feverishly generating new strains, which they hope will grow faster.