Abstract

Influenza A virus remains a major global health threat, with rapid mutation and emerging drug resistance underscoring the urgent need for novel antivirals. Manganese ions (Mn2+) are known to enhance host antiviral immunity, but their direct effects on influenza virus replication remain elusive. Here, we demonstrate that manganese chloride (MnCl2) potently inhibits the replication of both H1N1 and H3N2 subtypes in cultured cells at micromolar concentrations, with antiviral activity not shared by other divalent cations (Ca2+, Cu2+, Zn2+, Mg2+). Mechanistically, MnCl2 acts predominantly at post-entry stages, suppresses viral mRNA synthesis, and directly inhibits the RNA cleavage activity of the PA endonuclease. Pharmacological antagonism with the PA inhibitor baloxavir further supports PA as a key target. In a mouse model, intranasal MnCl2 administration alleviated body weight loss, reduced mortality, and decreased pulmonary viral RNA loads. Collectively, these findings identify Mn2+ as a direct inhibitor of influenza virus replication that acts, at least in part, by targeting the PA endonuclease, providing a conceptual framework for metal ion-based antiviral strategies.