Influenza virus is a widely studied pathogen as the causative agent of seasonal epidemics and occasional but unpredictable pandemics. It is a canonical enveloped virus which delivers its macromolecular contents to the host cell via membrane fusion . The lipid envelope of the influenza virions are decorated with hundreds of copies of the glycoprotein hemagglutinin (HA) which is necessary for attachment of the virions to cell surface sialic acid receptors (Figure ) . The influenza viral genome consists of eight single-stranded, negative sense RNA segments organized into macromolecular assemblies called viral ribonucleoproteins (vRNPs) . Electron microscopy studies on vRNPs have revealed that these are double helical structures 30-120 nm in length . Within the vRNPs, the RNA strand is bound to the nucleoprotein (NP) scaffold by interaction with its phosphodiester backbone such that, on average, there is 1 NP per 24 ribonucleotides . Inside the virions, the vRNPs associate with the matrix protein (M1) layer. Following binding to the cell surface receptors, the virions are endocytosed within endosomes. When the pH inside the endosome drops below 5.5, HA undergoes conformational change which triggers fusion between viral and endosomal membranes. Also, M2 channels pump protons to the viral interior leading to dissociation of the M1 layer from the viral membrane which in turn becomes more amenable to fusion . At the same time, the interaction between the M1 proteins and vRNPs weakens and the latter are released into the cytoplasm via a fusion porea process known as endosomal escape (Figure ) .