Antiviral siRNA (small interfering ribonucleic acid) lipid nanoparticle drug. Computer illustration showing a cross-section of a lipid nanoparticle carrying antiviral siRNA (orange) entering a human cell. Adding different molecules, such as plant lipids (phytosterols), to the nanolipid particle can change its shape and improve the delivery rate of the siRNA. This type of antiviral is being developed for use against Covid-19.