Why is H5N1 currently of major concern?

What we see at the moment is that the number of human cases is very small when compared with the magnitude of the outbreak in birds. Although this may suggest that the H5N1 virus is not easily transmitted from birds to humans, the virus could rapidly improve its capacity to transmit and cause the disease in humans. This can be done via two mechanisms:

• Exchange of genes, which is also known as reassortment. This could occur when humans or pigs are infected with two viruses at the same time - H5N1, and a circulating human influenza virus (which is capable of efficient transmission from person to person). This could lead to a new virus that can be efficiently transmitted from human-to-human.

• Mutation or change in the genetic characteristic of the virus. Mutational changes in the virus may result in the virus becoming more infectious to humans.

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