Table 2. Selected Mutations in the HA region of influenza A(H1N1)pdm09.

	Season
Mutation	4/2009–9/2009†	10/2009–3/2010	4/2010–9/2010	10/2010–3/2011	4/2011–9/2011	10/2011–3/2012	4/2012–9/2012	10/2012–3/2013	4/2013–9/2013	10/2013–12/2013
S69T*	S (100%)	S (99%)	S (100%)	S (100%)	S (100%)	T (71%)	T (68%)	S (98%)	S (100%)	S (100%)
P83S*	S (99%)	S (99%)	S (99%)	S (99%)	S (99%)	S (99%)	S (100%)	S (98%)	S (100%)	S (100%)
D97N	D (99%)	D (92%)	D (94%)	D (65%)	D (54%)	D (84%)	D (75%)	N (84%)	N (96%)	N (100%)
S143G*	S (100%)	S (100%)	S (99%)	S (77%)	S (68%)	G (82%)	G (75%)	S (86%)	S (96%)	S (100%)
K163Q	K (100%)	K (99%)	K (98%)	K (96%)	K (94%)	K (99%)	K (92%)	K (76%)	Q (64%)	Q (100%)
S185T*	S (99%)	S (99%)	S (84%)	T (68%)	T (76%)	T (89%)	T (98%)	T (96%)	T (100%)	T (100%)
A197T	A (99%)	A (96%)	A (90%)	A (62%)	A (55%)	T (82%)	T (75%)	A (86%)	A (96%)	A (100%)
S203T	T (67%)	T (96%)	T (100%)	T (100%)	T (100%)	T (99%)	T (98%)	T (98%)	T (100%)	T (100%)
V234I	V (100%)	V (99%)	V (100%)	V (99%)	V (100%)	V (100%)	V (98%)	I (70%)	V (69%)	V (100%)
A256T	A (100%)	A (99%)	A (100%)	A (100%)	A (100%)	A (99%)	A (100%)	A (91%)	T (66%)	T (100%)
N260D*	N (99%)	N (100%)	N (99%)	N (99%)	N (96%)	D (71%)	D (68%)	N (98%)	N (100%)	N (100%)
K283E*	K (99%)	K (98%)	K (100%)	K (97%)	K (98%)	K (98%)	K (95%)	E (73%)	E (93%)	E (100%)
I321V	V (98%)	V (94%)	V (100%)	V (99%)	V (98%)	V (98%)	V (95%)	V (97%)	V (99%)	V (95%)
E374K	E (97%)	E (62%)	K (79%)	K (84%)	K (98%)	K (98%)	K (98%)	K (98%)	K (100%)	K (100%)
S451N	S (99%)	S (99%)	S (83%)	N (69%)	N (77%)	N (88%)	N (95%)	N (97%)	N (99%)	N (100%)
E499K	E (100%)	E (99%)	E (93%)	E (89%)	E (85%)	E (92%)	E (90%)	K (84%)	K (97%)	K (100%)
V520A	V (100%)	V (98%)	V (97%)	V (99%)	V (99%)	A (72%)	A (68%)	V (88%)	V (96%)	V (100%)

Percentage refers to the percent of sequences in that season that have the noted amino acid.

^†Includes isolate collected 3/30/2009.

*Epitope residueβ.