**Abstract**

This chapter focuses on viral efficacy evaluations of silver ion (Ag<sup>+</sup> ) formulations against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the virus associated with the COVID-19 pandemic and feline calicivirus (FCV), a surrogate for human norovirus. The chapter discusses the proposed mechanism of inactivation, with reference to some previously published articles. In addition, it discusses the background/current trend/future view of Ag+ products that have been used widely as surface/environment disinfectants in daily life all over the world. In efficacy studies performed by using the standardized ASTM E1052 methodology, it was found that Ag+ formulated with a low concentration (26% w/w) of ethanol displayed virucidal activity against SARS-CoV-2 and FeCV. These formulations might be useful for preventing the transmission of such viruses and limiting the outbreaks of emerging infectious diseases caused by coronaviruses and caliciviruses. To our knowledge, this is the first report describing the virucidal efficacy of an Ag<sup>+</sup> formulation, evaluated by using the standardized ASTM E1052 methodology, for inactivating SARS-CoV-2. Some characteristics of Ag<sup>+</sup> -based virucides are discussed in this research report/minireview.

**Keywords:** COVID-19, feline calicivirus, liquid inactivation, SARS-CoV-2, silver ion (Ag<sup>+</sup> ), virucidal efficacy evaluation
