TABLE 2.

Summary of PB1-F2 truncations in H5N1 viruses^a

Yr of isolation	No. of viruses with PB1-F2 protein of indicated putative length (aa)													Total no. of viruses	% carrying truncated protein
	Truncated protein (≤78 aa)								Nontruncated protein (≥79 aa)
	0	8	11	24	25	34	57	63	79	81	87	90	101
1996												1		1	0
1997							2					17		19	10.5
1998												2		2	0.0
1999												11		11	0.0
2000												11		11	0.0
2001												39		39	0.0
2002											3	31		34	0.0
2003												61	1	62	0.0
2004											2	136	1	139	0.0
2005			1									242		243	0.4
2006	1	2		1			1				1	316		322	1.6
2007		3	1		2	1	2	1	2	1		323		336	3.0
2008	2	1			2		4		2	3		167	1	182	4.9
2009	4				16							106	2	128	15.6
2010		1		12	7		1			1	2	129		153	13.7
2011	1		2	3	11		12				1	164		194	14.9
2012	2				3		7		2			52	1	67	17.9
2013							14					9		23	60.9
Totals	10	7	4	16	41	1	43	1	6	5	9	1,817	6	1,966
	123								1,843					1,966	6.7

^aPB1 sequences from highly pathogenic H5N1 influenza viruses were retrieved from the NCBI, GISAID, and CDC databases. Sequences were aligned using MAFFT, and PB1-F2 sequence lengths were inferred from the sequences. Sequences were sorted by year of isolation and PB1-F2 protein length. The sequences expressing a protein of 78 aa or smaller were annotated as truncated.