As Merck & Co and Pfizer Inc prepare to report clinical trial results for experimental Covid-19 antiviral pills, rivals are lining up with what they hope will prove to be more potent and convenient oral treatments of their own.

Enanta Pharmaceuticals, Pardes Biosciences, Japan's Shionogi & Co Ltd and Novartis AG said they have designed antivirals that specifically target the coronavirus while aiming to avoid potential shortcomings such as the need for multiple pills per day or known safety issues.

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