This disclosure is directed to methods of using compositions comprising protocatechuic acid (PCA) to kill virus including a Covid-19 virus. The compositions generally comprise protocatechuic acid, a liquid vehicle, and a stabilizer. In embodiments, the liquid vehicle comprises an alcohol and/or water. In preferred embodiments, the oil is an essential oil. In embodiments, the compositions may comprise principally protocatechuic acid, liquid vehicle, and stabilizer as the main ingredients. The compositions may be sprayed onto various products and articles of manufacture, and mammalian and human skin, to kill virus including a Covid-19 virus and to further protect the product or human skin for a period of time up to 24 hours or more. In preferred embodiments, an alcohol component kills virus on contact, and after drying, the residual surface PCA coating provides a continuing anti-viral function.