TABLE 1.

The six highly pathogenic avian influenza H5N1 viruses analyzed in this study^a

Virus strain	Abbreviation	Clinical outcome of patient	HA clade	Receptor-binding specificityb		PB1-F2	PB2			NS1
				α2,3	α2,6	66	591	627	701	92	C terminus
A/Vietnam/UT3028II/2004 clone3	VN3028IIcl3	Died	1	++++	++++	N	Q	K	D	D	ESEV
A/Vietnam/UT30259/2004	VN30259	Died	1	++++	++	N	Q	K	D	D	ESEV
A/Vietnam/UT3040/2004	VN3040	Died	1	++++	–	N	Q	K	D	D	10-aa deletion
A/Vietnam/UT3062/2004	VN3062	Died	1	++++	–	N	Q	K	D	D	ESEV
A/Vietnam/30408/2005 clone7	VN30408cl7	Recovered	1	++++	+++	N	Q	K	D	D	ESEV
A/Vietnam/UT30850/2005	VN30850	Died	2.3.4	++++	–	N	Q	K	D	D	ESEV

^aFor PB1-F2, PB2, and NS1, the amino acid at the position(s) indicated in the subheadings is specified.

^bThe level of receptor-binding affinity is indicated using a “+/−” scale, where “−” indicates no receptor binding affinity, “+” indicates affinity, and the number of “+” symbols indicates the intensity of the receptor-binding affinity (21).