Susceptibility of influenza B viruses to neuraminidase inhibitors during 2014 to 2015 in mainland China

Objective To analyze the phenotypic characteristics of antiviral-resistant influenza B viruses circulating in mainland China and to analyze the susceptibility of influenza B viruses to neuraminidase inhibitors (NAIs). Methods Antiviral-resistant phenotyping test was performed to analyze the NAI susceptibility of 1 386 influenza B viruses isolated in mainland China from April 2014 to March 2015, including the test of susceptibility to oseltamivir and zanamivir. Results All of the 94 B-Victoria lineage viruses were sensitive to oseltamivir and zanamivir. Of all 1 292 B-Yamagata lineage viruses tested, 1 virus showed reduced sensitivity to oseltamivir with NA gene containing I221T amino acid mutation, 10 viruses showed reduced sensitivity to zanamivir with 4 having D197N amino acid mutation in NA gene, 3 viruses showed reduced sensitivity to both oseltamivir and zanamivir with NA gene possessing D197N amino acid mutation and 1 virus carrying the A245T amino acid mutation in NA gene showed reduced sensitivity to oseltamivir and highly reduced sensitivity to zanamivir. Conclusion The majority of influenza B viruses circulating in mainland China during 2014 to 2015 were sensitive to NAIs, which indicated that NAIs could be used continually for clinical treatment of patients with influenza. Sustained monitoring of antiviral susceptibility of influenza B viruses should be emphasized for timely detection of antiviral resistant viruses and more attention should be paid to the D197N mutations in NA gene of influenza B viruses. Key words: Influenza B virus; Neuraminidase inhibitor; Susceptibility