A-Z Index × Submit A-Z Index × Submit A-Z Index Search Dropdown × Submit Facebook Twitter LinkedIn Syndicate Emerging Infectious Disease journal ISSN: 1080-6059 Disclaimer: Early release articles are not considered as final versions. Any changes will be reflected in the online version in the month the article is officially released.
Highly pathogenic avian influenza A(H5N1) clade 2.3.4.4b virus continues to cause animal outbreaks and sporadic zoonotic infections. In a mouse model of lethal influenza disease, we compared oseltamivir, baloxavir, and molnupiravir monotherapies with 2-drug combinations. Baloxavir-based combinations improved survival, reduced lung viral loads, and prevented extrapulmonary dissemination, supporting H5N1 preparedness strategies.
Highly pathogenic avian influenza A(H5N1) clade 2.3.4.4b virus continues to cause widespread outbreaks and sporadic zoonotic infections, underscoring the need to optimize antiviral strategies ( 1 – 3 ). Licensed influenza antiviral drugs can reduce disease severity but might be compromised in severe infections by high viral burdens, treatment delays, and treatment-emergent resistance, motivating evaluation of combination regimens ( 4 – 7 ). Recent H5N1 treatment studies using mouse models suggest antiviral performance can vary by exposure route and disease progression ( 8 – 11 ). To inform preparedness-oriented selection, we compared direct-acting antiviral drugs from distinct classes in a lethal mouse model. We tested monotherapies and 2-drug combinations of 2 licensed influenza antiviral agents, oseltamivir phosphate (OSP; neuraminidase inhibitor) and baloxavir acid (BXA; cap-dependent endonuclease inhibitor), and molnupiravir (MPV; nucleoside analog) to assess whether combinations provided synergistic benefit.
Figure 1 . Therapeutic efficacy of baloxavir-based combinations and monotherapies for treating influenza A(H5N1) clade 2.3.4.4b virus infection in mice. Drug names and doses are provided in the keys (e.g., BXA+MPV 20+25 mg/kg...
We challenged 6- to 8-week-old female BALB/c mice intranasally with A/mink/Spain/3691–8_22VIR10586–10/2022 (5 LD 50 [50% median lethal dose]) in a 50-µL inoculum (90 TCID 50 [50% tissue culture infectious dose]) ( Appendix ). We treated mice at 6 hours postinfection (hpi). We administered OSP and MPV orally twice daily for 5 days and administered BXA once subcutaneously. For the low-dose comparison, mice received OSP 25 mg/kg, MPV 25 mg/kg, or BXA 20 mg/kg, and corresponding 2-drug pairs at the same dosages: OSP/MPV, BXA/OSP, BXA/MPV. We monitored body weight and survival through 18 days postinfection (dpi) (n = 7) and quantified infectious virus titers in lung, brain, and heart by TCID 50 assay at 4 and 6 dpi (n = 3/time point) ( Figure 1 ; Appendix Tables 1–5).
Vehicle-treated mice exhibited rapid weight loss and uniform death. In monotherapy low-dose treatments, OSP or MPV conferred partial protection (2/7 survival each), whereas BXA administered as a single dose was more protective (4/7 survival) and more consistently limited weight loss ( Figure 1 , panels A–F). Dose-escalation to 50 mg/kg monotherapies also improved outcomes but did not provide 100% protection ( Appendix Figures 2, 3), consistent with prior reports showing therapeutic benefit of antiviral drugs in H5N1 mouse infection models ( 8 – 11 ). Accordingly, we evaluated 2-drug regimens in which BXA was maintained at 20 mg/kg and partnered with OSP or MPV at either 25 or 50 mg/kg. Ac…