An in Vitro Short-Term Treatment with Black Tea-Derived Theaflavins Reduced Infectivity of SARS-CoV-2 in Saliva

The coronavirus disease 2019 is caused by the etiological agent severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). SARS-CoV-2 is abundant in the saliva of an infected person; therefore, saliva is an important source of infection. The present study evaluated the efficacy of short-term treatment using tea-derived compounds against SARS-CoV-2 infectivity in the saliva. The antiviral efficacy of theaflavin 3,3’-gallate (TF3) and two black tea-derived theaflavin concentrates (TF35 and TF80) against a prototype Wuhan and a recent Omicron strain was evaluated using human saliva. TF3, TF35, and TF80 reduced the infectivity of both strains at high (1 mM or 1 mg/ml) and low (0.25 mM or 0.25 mg/ml) concentrations; however, antiviral efficacy against the Wuhan strain was stronger than that against the Omicron strain. Furthermore, the antiviral agents at high concentrations showed better efficacy against both strains than those at low concentrations. For example, treatment with 1 mM TF3 for 10 min decreased the infectivity of Wuhan and Omicron strains to approximately 0.05% and 3%, respectively; these reduction rates are attributable to the inactivation of large amounts of viruses (9.995 × 105 and 9.7 × 104 TCID50, respectively). Considering these facts, it was expected that the inclusion of the main components of black tea (TF3) and the black tea-derived theaflavin concentrates (TF35 and TF80) in the oral cavity for a short time might inactivate the virus in saliva and, thus, can be considered an effective suppressor of the spread of infection.