In a recent publication,1 he and his team described their identification of a variant of influenza previously unseen in humans, and discussed its implications for the development of a new pandemic strain. Influenza has caused serious disease in humans throughout recorded history, principally due to the inherent 'variability' of the virus itself. This variation in the virus comes about by two mechanisms - 'antigenic drift' and 'antigenic shift'. Hence, antigenically drifted forms of influenza may cause new waves of infection on a regular basis. The human population is therefore highly sensitive to shifted influenza strains, since we are effectively unguarded immunologically against them.
Antigenic shift comes about because the genes of the influenza virus exist as discrete segments.
Thus, in a double infection with two different influenza viruses, genes from both may be mixed together and re-packaged into a third new virus, with characteristics of the two parents. Immunological defences in this case will be completely absent. It is speculated that a dramatic new antigenic shift will occur, but which viruses might be involved or when this might happen is unknown. It might be the re-introduction of a virus from the past, or a totally new form, originating from the reservoir of influenza viruses in birds. These viruses have 15 different HA and nine different NA proteins.