Effectiveness of baloxavir marboxil in nonhuman primates infected with highly pathogenic avian influenza A(H7N9) virus.

BACKGROUND

Highly pathogenic avian influenza (HPAI) A(H7N9) virus poses a potential public health threat, underscoring the need for effective antiviral options for outbreak preparedness. Baloxavir marboxil (BXM) is a cap-dependent endonuclease inhibitor approved for seasonal influenza, but its in vivo efficacy against HPAI A(H7N9) virus has not been fully evaluated.

METHODS

We evaluated the efficacy of BXM in cynomolgus macaques infected with a reverse genetics-generated HPAI A(H7N9) virus. Animals received either low- or high-dose BXM, single-dose oseltamivir, or vehicle at 4 or 48 h post-infection (hpi). BXM administration was designed to mimic human pharmacokinetics. Viral titres, body temperature, body weight, lung pathology, and treatment-emergent viral substitutions were analysed.

FINDINGS: Early treatment (4 hpi) with BXM significantly reduced viral titres in nasal and tracheal swabs, lessened weight loss, and decreased pulmonary inflammation and alveolar damage compared to untreated or oseltamivir-treated animals. Virus pathogenicity was relatively mild; no animals died. Delayed treatment (48 hpi) showed limited benefit. The PA-I38T (83.8%) and PA-E23G (78.6%) substitutions associated with BXM resistance were detected in one animal, and a PA-K34R (85.4%) substitution was detected in another animal. These substitutions reduce BXM susceptibility and were detected at low titres.

INTERPRETATION: Although the dosing regimen used in this study involved repeat dosing to achieve the plasma drug concentrations after a single dose in humans, these findings highlight the importance of early antiviral intervention and support BXM use as a potential countermeasure against HPAI A(H7N9) virus infection, as resistance-associated substitutions remained limited in the macaque model. BXM may be a valuable therapeutic option for HPAI A(H7N9) virus infections.

FUNDING: Supported by the Japan Agency for Medical Research and Development (JP20wm0125002, JP223fa627001) and Shionogi & Co., Ltd.