Identification of a human influenza type B strain with reduced sensitivity to neuraminidase inhibitor drugs

Abstract

A total of 126 influenza B isolates isolated between 1998 and 2002 from Australasia and the Asia-Pacific region were tested for their sensitivity to the neuraminidase (NA) inhibitor drugs zanamivir and oseltamivir carboxylate using a fluorescence-based enzyme assay. The mean (±1 S.D.) 50% inhibitory concentration (IC50) of the influenza B viruses tested was 1.41±0.53 nM against zanamivir and 14.91±14.31 nM with oseltamivir carboxylate. However, a single type B isolate (B/Perth/211/2001) from an infant who had not been treated with either of the NA inhibitor drugs, showed a nine-fold lower sensitivity to zanamivir and a 14-fold lower sensitivity to oseltamivir carboxylate compared with the me..