5. B/Victoria-lineage viruses showing RI or HRI
Of 604 B/Victoria-lineage viruses tested, 12 (2%) showed RI or
HRI by one or more of the NAIs (Fig. 2 and Table 1). One B/
Victoria-lineage virus from Bangladesh with a NA E117G substitution
showed HRI by three of the four NAIs tested with a 2326-foldincrease in peramivir IC50, a 1010-fold increase in zanamivir IC50, a
649-fold increase in laninamivir IC50 and RI with a 12-fold increase
in oseltamivir IC50 compared to values for B/Victoria-lineage viruses
displaying NI by the four NAIs (Table 1). NA amino acid substitutions
N151S and D197N were detected in B/Yamagata-lineage
HA – B/Victoria-lineage NA reassortants. All other substitutions
identified in the isolates that were classified as having RI to zanamivir
or peramivir require further analysis to assess whether the
amino acid substitutions observed are responsible for the changes
in IC50. Three B/Victoria-lineage viruses had IC50 values that were
close to the intersect between NI and RI categories for zanamivir
or peramivir, but no NA amino acid substitutions were detected
on sequencing.