Neuraminidase inhibitor susceptibility testing of influenza type B viruses in China during 2010 and 2011 identifies viruses with reduced susceptibility to oseltamivir and zanamivir

abstract Influenza type B viruses are responsible for substantial morbidity and mortality in humans. Antiviraldrugs are an important supplement to vaccination for reducing the public health impact of influenzavirus infections. Influenza B viruses are not sensitive to M2 inhibitors which limit the current therapeuticoptions to two neuraminidase inhibitors (NAIs), oseltamivir and zanamivir, which are licensed in manycountries. Drug resistance is a public health concern which has necessitated monitoring of influenza virusdrug susceptibilities through active global surveillance. Here, we report the results of drug susceptibilitysurveillance of influenza type B viruses (n = 680) collected in mainland China during two calendar years,2010 and 2011, assessed using functional neuraminidase (NA) inhibition (NI) assays. Four influenza Bviruses exhibited reduced susceptibilities to oseltamivir, but not zanamivir, and shared the amino acidsubstitution I221T (ATC ? ACC), at this conserved residue in the NA active site (I222T in N2 numbering).Additionally, a single virus with reduced susceptibility to both oseltamivir and zanamivir was identifiedand contained an amino acid substitution D197N (GAC ? AAC) at another conserved residue in the NAactive site (D198N in N2 numbering). This report underlies the importance of continued influenzaantiviral susceptibility surveillance globally, even in countries where the use of NAIs has been low ornon-existing. 2012 Elsevier B.V. All rights reserved.