http://ecdc.europa.eu/en/publications/P ... sation.pdf
Six genetic groups can be defined for the circulating H1N1 viruses. These groups can be defined by the amino acid substitutions:
i) N125D, observed originally as an emerging genetic group in the Southern Hemisphere and subsequently widespread in the Northern Hemisphere and exemplified by the reference virus A/Christchurch/16/2010;
ii) D97N and S185T, e.g. A/England/676/2010;
iii) S143G, S185T and A197T, e.g. A/Baden-Wurtemburg/14/2010 or A/Brussels/S0004/2011;
iv) A134T and S183P, e.g. A/Alborz/5607/2010;
v) D97N, R205K, I216V and V249L, e.g. A/Trieste/11/2011;
vi) N31D, S162N (adding a glycosylation site) and A186T, e.g. A/Czech Republic/32/2011
The viruses highlighted in Table 2 as included in the HA gene phylogenetic analysis belong to genetic groups (i) and (ii) but viruses from each of the genetic groups have been collected in EU and EU-affiliated countries.
As previously, encoded periodic amino acid substitutions or polymorphisms at amino acid residues 153-157, 222 and 223 are marked on the phylogenetic tree. Substitutions at residues 153-157 in the HA are commonly associated with reduced titres in HI assays and often the substitution or polymorphism was not seen when the nucleotide sequence of the corresponding clinical specimen has been analysed. This indicates that polymorphism at residues 153-157 is often a result of cell culture.
Substitution and polymorphism at amino acid residue 222 continues to be detected and the change D222G has been postulated to be detected more often in viruses recovered from patients suffering with severe disease.
Substitutions at residue 223 (Q223R) have also been observed and are associated with isolation and propagation of virus in hens’ eggs.