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Volume 31, Number 4—April 2025

Research

Antiviral Susceptibility of Influenza A(H5N1) Clade 2.3.2.1c and 2.3.4.4b Viruses from Humans, 2023–2024

Philippe Noriel Q. Pascua1, Anton Chesnokov1, Ha T. Nguyen, Han Di, Juan De La Cruz, Yunho Jang, Andrei A. Ivashchenko, Alexandre V. Ivachtchenko, Erik A. Karlsson, Borann Sar, Chin Savuth, Timothy M. Uyeki, Charles Todd Davis, and Larisa V. GubarevaComments to Author 
Author affiliation: Centers for Disease Control and Prevention, Atlanta, Georgia, USA (P.N.Q. Pascua, A. Chesnokov, H.T. Nguyen, H. Di, J.D.L. Cruz, Y. Jang, T.M. Uyeki, C.T. Davis, L.V. Gubareva); ChemDiv, San Diego, California, USA (A.A. Ivashchenko, A.V. Ivachtchenko); Avisa LLC, Hallandale Beach, Florida, USA (A.V. Ivachtchenko); Virology Unit, Institut Pasteur du Cambodge, Phnom Penh, Cambodia (E.A. Karlsson); US Centers for Disease Control and Prevention Country Office, Phnom Penh (B. Sar); National Institute of Public Health, Ministry of Health, Phnom Penh (C. Savuth)

Main Article

Table 3

NA inhibitor susceptibility of highly pathogenic avian influenza A(H5N1) viruses isolated from humans in fluorescent NA inhibition assay, 2023–2024 *

Influenza A(H5N1) virus Mean IC50, nM (fold change)
Oseltamivir Zanamivir Peramivir Laninamivir AV5080
Clade 2.3.2.1c, median IC50, n = 7 0.96 0.18 0.10 0.18 0.07
  A/Cambodia/NPH230032/2023 0.78 ± 0.18 0.20 ± 0.05 0.08 ± 0.02 0.12 ± 0.03 0.05 ± 0.02
  A/Cambodia/2302009/2023 1.00 ± 0.09 0.24 ± 0.04 0.09 ± 0.03 0.16 ± 0.03 0.05 ± 0.02
  A/Cambodia/NPH230776/2023 0.74 ± 0.16 0.17 ± 0.03 0.11 ± 0.03 0.18 ± 0.04 0.07 ± 0.01
  A/Cambodia/KSH230332/2023 1.03 ± 0.25 0.18 ± 0.02 0.12 ± 0.02 0.21 ± 0.04 0.08 ± 0.02
  A/Cambodia/2311257/2023 0.99 ± 0.40 0.18 ± 0.02 0.10 ± 0.02 0.18 ± 0.02 0.07 ± 0.00
  A/Cambodia/24020155/2024 0.96 ± 0.16 0.20 ± 0.01 0.10 ± 0.02 0.17 ± 0.02 0.06 ± 0.01
  A/Cambodia/24020179/2024
 0.90 ± 0.13
 0.18 ± 0.02
 0.10 ± 0.01
 0.17 ± 0.01
 0.06 ± 0.01
Clade 2.3.4.4b, median IC50, n = 7 3.61 0.20 0.08 0.16 0.04
  A/Chile/25945/2023 2.98 ± 0.53 0.20 ± 0.02 0.09 ± 0.01 0.19 ± 0.03 0.04 ± 0.01
  A/Texas/37/2024 3.16 ± 0.62 0.22 ± 0.03 0.10 ± 0.03 0.19 ± 0.03 0.04 ± 0.01
  A/Michigan/90/2024 3.65 ± 0.71 0.19 ± 0.03 0.08 ± 0.02 0.16 ± 0.04 0.04 ± 0.01
  A/Colorado/109/2024 3.99 ± 0.15 0.20 ± 0.02 0.08 ± 0.01 0.17 ± 0.03 0.03 ± 0.01
  A/Colorado/137/2024 3.80 ± 0.15 0.19 ± 0.06 0.07 ± 0.00 0.16 ± 0.02 0.03 ± 0.00
  A/Colorado/139/2024 3.51 ± 0.72 0.18 ± 0.03 0.07 ± 0.01 0.16 ± 0.03 0.03 ± 0.00
  A/California/134/2024
 3.61 ± 0.52
 0.21 ± 0.02
 0.07 ± 0.01
 0.16 ± 0.02
 0.04 ± 0.01
Control viruses†
  A/bald eagle/FL/2022 (H5N1)‡ 3.07 ± 0.64 0.20 ± 0.04 0.09 ± 0.02 0.17 ± 0.03 0.04 ± 0.01
  A/Illinois/45/2019 (H1N1)pdm09 0.34 ± 0.10 0.16 ± 0.04 0.05 ± 0.01 0.17 ± 0.01 0.07 ± 0.01
  A/Alabama/03/2020 (H1N1)pdm09, NA-H275Y 201.27 ± 44.79 (592) 0.25 ± 0.06 (2) 15.80 ± 2.74 (316) 0.38 ± 0.04 (2) 0.78 ± 0.14 (11)
  A/Pennsylvania/46/2015 (H3N2) 0.15 ± 0.01 0.22 ± 0.04 0.08 ± 0.01 0.35 ± 0.08 0.27 ± 0.04
  A/Washington/33/2014 (H3N2), NA-E119V 47.33 ± 6.18 (315) 0.42 ± 0.05 (2) 0.11 ± 0.01 (1) 0.48 ± 0.09 (1) 0.16 ± 0.03 (1)
  B/North Carolina/25/2018 (Vic) 23.70 ± 1.83 1.97 ± 0.63 0.55 ± 0.07 1.64 ± 0.13 0.87 ± 0.12
  B/Missouri/12/2018 (Vic), NA-D197E 165.21 ± 20.39 (7) 13.12 ± 4.95 (7) 8.01 ± 0.3.11 (15) 5.20 ± 2.27 (3) 2.20 ± 0.52 (3)

*Data shown are means +SDs of >3 experiments. Fold change was calculated from the subtype sequence-matched control virus. IC50, 50% inhibitory concentration; NA, neuraminidase. †Control seasonal influenza A viruses were from the Centers for Disease Control and Prevention Neuraminidase Inhibitor Susceptibility Reference Virus Panel International Reagent resource (no. FR-1755 ver3). ‡Clade 2.3.4.4b influenza A(H5N1) virus, A/bald eagle/Florida/W22–134-OP/2022 (GISAID ID no. EPI_ISL_15063846; https://www.gisaid.org), was used as a control.

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1These first authors contributed equally to this article.

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