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Volume 23, Number 4—April 2017


Antiviral Drug–Resistant Influenza B Viruses Carrying H134N Substitution in Neuraminidase, Laos, February 2016

Tatiana Baranovich, Phengta Vongphrachanh, Pakapak Ketmayoon, Thongchanh Sisouk, Khampheng Chomlasack, Viengphone Khanthamaly, Ha Thuy Nguyen, Vasiliy P. Mishin, Henju Marjuki, John R. Barnes, Rebecca J. Garten, James Stevens, David Wentworth, and Larisa V. GubarevaComments to Author 
Author affiliations: Carter Consulting, Inc., Atlanta, Georgia, USA (T. Baranovich); World Health Organization Collaborating Center for Surveillance, Epidemiology and Control of Influenza, Atlanta (T. Baranovich, V. Khanthamaly, H.T. Nguyen, V.P. Mishin, H. Marjuki, J.R. Barnes, R.J. Garten, J. Stevens, D.E. Wentworth, L.V. Gubareva); Centers for Disease Control and Prevention, Atlanta (T. Baranovich, V. Khanthamaly, H.T. Nguyen, V.P. Mishin, H. Marjuki, J.R. Barnes, R.J. Garten, J. Stevens, D.E. Wentworth, L.V. Gubareva); National Center for Laboratory and Epidemiology, Vientiane, Laos (P. Vongphrachanh, P. Ketmayoon, T. Sisouk, K. Chomlasack); World Health Organization Emerging Disease Surveillance and Response Unit, Vientiane, Laos (P. Ketmayoon); Battelle Memorial Institute, Atlanta (H.T. Nguyen)

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Table 1

Neuraminidase inhibitor susceptibility of influenza B viruses isolated from human respiratory specimens. Laos, 2016*

Virus isolate
NA amino acid change§
Mean IC50 ± SD, nmol/L (fold change)†‡
Date specimen collected
GISAID accession no.
B/Laos/0080/2016 H134 1.09 ± 0.16 (1) 14.48 ± 1.76 (1) 0.36 ± 0.05 (1) 1.15 ± 0.02 (1) 14 Jan EPIISL 222862
B/Laos/0406/2016 H134N 148.36 ± 14.40 (129) 37.87 ± 1.96 (4) 31.09 ± 3.70 (74) 62.43 ± 4.66 (42) 9 Feb EPIISL 230596
B/Laos/0525/2016 H134N 176.03 ± 11.14 (158) 37.55 ± 5.60 (4) 30.25 ± 2.90 (72) 60.12 ± 2.38 (41) 15 Feb EPIISL 230599
B/Laos/0654/2016 H134N 151.95 ± 16.30 (138) 35.06 ± 5.08 (4) 31.29 ± 0.24 (75) 61.53 ± 1.03 (42) 25 Feb EPIISL 230600

*Viruses were isolated and propagated on MDCK cells. Susceptibility was determined using a fluorescence-based neuraminidase (NA) inhibition assay.
†IC50 values (NA inhibitor concentration needed to reduce NA activity by 50%) represent mean ± SD from 3 independent experiments.
‡Fold change compared with the median IC50 value determined for influenza B-Victoria lineage viruses (n = 430) that were circulating worldwide during the 2015‒16 influenza season. Median IC50 values are 1.11, 9.67, 0.42, and 1.47 nM for zanamivir, oseltamivir, peramivir, and laninamivir, respectively. Bold indicates fold increases that correspond to reduced inhibition (5- to 50-fold) or to highly reduced (>50-fold) inhibition by a NAI, as outlined by the World Health Organization Expert Working Group of the Global Influenza Surveillance and Response System for Surveillance on Antiviral Susceptibility (5).
§Amino acid residue 134 in influenza type B NA corresponds to residue Q136 in N1 and N2 NA amino acid numbering (6).
¶Oseltamivir carboxylate was used in NA inhibition assay.

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