Fig. 1.

—Experimental set-up. In each of three replicates, influenza A virus was serially passaged in MDCK cells and exposed to increasing concentrations of either oseltamivir only, or of oseltamivir and favipiravir combined, from passage 4 onwards. The multiplicity of infection (MOI) used to seed each passage is shown on the right hand side. ED₅₀ represents a 50% effective dose for drug-naïve virus. The MOIs are valid for all replicates except combined drug and oseltamivir replicate 1 passage 10, where an MOI of 0.005 was applied.