Time is critical when developing vaccines or drug treatments; new drugs typically take many years to reach the clinic. Repurposing existing drugs, clinical trials candidates, and approved natural products, that have been in man and whose toxicity, pharmacokinetics, and metabolism is already well understood, is a rational and rapid way to find effective therapies during a pandemic . Repurposing can be done by high throughput in vitro assays, in vivo studies in animals, and computational drug design methods. Several teams have undertaken wet-lab screening of existing drugs against viral targets or viral assays, but none have achieved sufficient high throughput to allow >10,000 candidates to be assessed. Computational screening can be performed easily on large numbers of molecules, with relative binding affinities allowing ranking of the candidates for focused in vitro and in vivo testing followed by human antiviral trials, with minimal delay .