Edwards, L.E., D.C. Nguyen, X. Lu, H. Hall, A. Balish, J.E. Mabry, W. Lim,
N.J. Cox, A. Klimov, and J.M. Katz (2004). Antigenic characteristics of
recent avian influenza A H5N1 viruses isolated from humans. International
Congress Series 1263: 109-113.

http://cmbi.bjmu.edu.cn/news/report/2005/flu/4.pdf

Abstract: Background: In February 2003, highly pathogenic
avian influenza A H5N1 viruses reemerged in humans. Despite
repeated outbreaks in domestic poultry in Hong Kong since
1999, this was the first isolation of H5N1 from humans since
the outbreak in Hong Kong in 1997, which resulted in 18 human
cases and 6 deaths.

Methods: To better understand the antigenic relationship between the 2003
H5N1 human virus A/Hong Kong/213/03 (HK/213) and other H5 viruses,
post-infection ferret sera or post-infection human sera were tested for
reactivity by hemagglutination-inhibition and microneutralization assays
with H5N1 viruses circulating in Hong Kong or elsewhere in Asia since
1997.

Results: The H5N1 virus isolated from a 9-year-old male in Hong Kong was
antigenically distinguishable from recent H5N1 viruses isolated from wild
birds in Hong Kong and from the human 1997 H5N1 viruses, using
post-infection ferret sera. Likewise, sera from this case patient,
collected 22 days post-symptom onset, reacted to high titers with the
homologous HK/213 virus, but gave eightfold lower titers with A/Hong
Kong/156/97, and other H5 viruses. Conclusion: These results suggest that
this recent human H5N1 virus is antigenically distinguishable from current
and previously circulating H5N1 viruses from Asia, including the viruses
previously isolated from humans.