TABLE 5.

Characterization of extreme and mild outliers detected among influenza B viruses from three previous seasons

SeasonStrainMean IC50 ± SD (nM)aOutlier(s)/drug(s)bNA mutationcAccession no.
OseltamivirZanamivir
2004-2005B/Hong Kong/36/20051,778.25 ± 729.78d154.85 ± 47.47dE/O, E/ZR371KEU879085
2004-2005B/Michigan/20/200510.80 ± 2.90e1.54 ± 0.27M/OH274YCY015375
2004-2005B/California/5/200510.48 ± 1.628.65 ± 1.46M/OI222TEU879086
2004-2005B/California/4/20058.60 ± 1.933.73 ± 1.72M/OT325IEU879084
  • a Mean IC50 ± SD values were calculated from data collected from at least three independent experiments.

  • b E, extreme; M, mild; O, oseltamivir (IC50 values of >7.47 nM); Z, zanamivir (IC50 values of >11.29 nM).

  • c Boldface type indicates the mutation in the NA active site.

  • d A 407-fold increase in IC50 to oseltamivir and a 29-fold increase in IC50 to zanamivir compared to the IC50 values of the matching virus B/Hong Kong/45/2005 (accession no. ISDN127249).

  • e A 4-fold increase in IC50 to oseltamivir compared to that of the matching virus B/Illinois/47/2005 (accession no. CY15376).