Mapping the antigenic evolution of an H5N1 clade 2.2 A/chicken/ Egypt/1709-1/07 and the drift variant A/chicken/Egypt/1709-6/08 by a sensitive pseudotyped-based assay

The propensity of influenza virus to mutate and evolve into new types

with divergent antigenic determinants is an important challenge in the

control of influenza infection. In Egypt, an H5N1 avian virus belonging

to clade 2.2 was notified in February 2006 and the country has faced

a huge number of outbreaks since. Subsequently, to control infection

in poultry and prevent the risk of human exposure, an inactivated

vaccine containing an H5 virus belonging to a different lineage to the

Eurasian H5N1 (H5N2/Mexico) was employed. Despite this, the

continuous circulation of the virus and the mass vaccination programme

has resulted in progressive genetic evolution and significant antigenic

drift with multiple mutations near the major antigenic sites leading

to the emergence of a new strain grouped within clade 2.2.1. To

establish whether the administration of the H5N2/Mexico vaccine

is likely to provide cross-protective antibody responses against

different clades, lentiviral pseudotypes derived from H5N1 HPAI

viruses (A/Egypt-1709-01/2007) and the antigenic drift variant (A/

Egypt-1709-06/2008) were constructed and used in pseudotype-based

neutralisation (pp-NT) assays. Overall results indicated a significantly

lower level of antigenic cross-reactivity of post vaccine sera against the

pseudotyped-particles bearing the HA of the 1709-06 drift variant.