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The frequency of the NS1 N92D substitution from 1980 to 2015 in influenza B viruses. (a) Frequency changes of the NS1 N92D substitution and the total count of isolates in each year from 1980 to 2015. (b) Global count of residues at positions 92 and 93 of NS1 from Influenza B viruses. Count of residues from all 5285 Influenza B sequences from 1940 to 2015. The N92D substitution represents a frequency of 6.6 % in all Influenza B NS1 sequences.
