Table 2.
Antigenic drift events and associated amino acid substitutions in H3N2 (1968–2015) and H1N1 (1977–2009) seasonal influenza A viruses
| Subtype | Antigenic drift eventa | Predominant amino acid substitution(s) in HA (antibody binding sites)b |
| H3N2 [71, 76–80] | HK68→EN72 | G144D (A) |
| EN72→VI75 | S145N(A), S193D (B) | |
| VI75→TX77 | D53K(C), E82K(E) | |
| TX77→BK79 | K156E(B) | |
| BK79→SI87 | Y155H(B), K189R(B) | |
| SI87→BE89 | G135E(A), N145K(A), N193S(B) | |
| BE89→BE92 | E135K(A), K145N(A), E156K(B) | |
| BE92→WU95 | N145K(A), G172D(D) | |
| WU95→SY97 | K62E(E), K156Q(B), E158K(B) | |
| SY97→FU02 | Q156H(B) | |
| FU02→CA04 | K145N(A), Y159F(B) | |
| CA04→BR07 | S193F(B), D225N (near D) | |
| BR07→PE09 | K158N(B), N189K(B) | |
| PE09→TX12 | N278K(C), S45N(C) | |
| TX12→SW13 | N145S(A), N225D(near D), A138S(A), F159S(B) | |
| TX12→HK14 | N145S(A), N225D(near D), N144S(A), F159Y(B), Q311H(C), K160T(B) | |
| H1N1 [81] | CH83→SI86 | K197T(Sb), K192R(Sb) |
| SI86→TE91 | K82E(Cb) | |
| TE91→BE95 | T132V(Near Sa), S273P(Pa) | |
| BE95→NE99 | E156G(Sa), S77L(Cb) | |
| NE99→BR07 | T197K(Sb), R192M(Sb), K144E(Ca2), S46N(Pb) | |
| NE99→SO06 | E276K(Pa), R192K(Sb), K144E(Ca2), Y101H(near Cb) |
aFor H3N2 viruses: HK68, A/Hong Kong/1/1968; EN72, A/England/42/1972; VI75, A/Victoria/3/1975; TX77, A/Texas/1/77; BK79, A/Bangkok/01/1979; SI87, A/Sichuan/2/1987; BE89, A/Beijing/352/1989; BE92, A/Beijing/32/1992; WU95, A/Wuhan/359/1995; SY97, A/Sydney/5/1997; FU02, A/Fujian/411/2002; CA04, A/California/07/2004; BR07, A/Brisbane/59/2007; PE09, A/Perth/16/2009; TX12, A/Texas/50/2012; SW13, A/Switzerland/9715293/2013; HK14, A/Hong Kong/4801/2014. For H1N1 viruses: CH83, A/Chile/1/83; SI86, A/Singapore/6/1986; TE91, A/Texas/36/91 BE95, A/Beijing/262/95; NE99, A/New Caledonia/20/1999; BR07, A/Brisbane/59/2007; SO06, A/Solomon Islands/3/2006
bAll positions are under H3 numbering