In vitro antiviral assays are used to evaluate the efficacy of antiviral compounds against specific viruses within a controlled cell culture environment. In vitro antiviral assays play a pivotal role in the discovery and optimization of new antiviral therapies. Commonly used in vitro assays include plaque reduction assays, TCID50 assays, and MTT assays, each offering different methods to quantify viral activity and cell viability. These assays are crucial in the early stages of drug development, as they help identify promising antiviral candidates before advancing to in vivo studies and clinical trials.