Antigenic and amino acid sequence variation among different clades of H5N1 vaccine candidate viruses.

aHemagglutination inhibition (HI) titers were determined using turkey red blood cells.
bTiters for homologous antigen/antisera are shown with values underlined. Titers are presented as the geometric mean titers (GMT) calculated from five independent HI tests.
cDifferences among strain-specific cross reactivity are quoted as dilutions relative to that of the end-point dilution value for the homologous antigen/sera response. Viruses are considered antigenically diverse if titers are reported as ≥8-fold difference in two-way tests.
dOnly a reassortant virus for Hubei10 was used in assay. Others were wild type viruses.
eAmino acid sequence identities were calculated for the 267 residues of the HA1 structural domain (residues 34–300) of the mature HA, using CLUSTALX [84].
fSurface residue differences were quantified for the HA1 structural domain (residues 34–300) of the mature HA monomer. For this analysis, 166 of the 267 residues were considered surface residues. The number of surface residue substitutions is given in parentheses.