In vivo effect of mouthwashes on viable viral load of SARS-CoV-2 in saliva: a pilot study

Current data on the efficacy of antiseptic mouthwashes to reduce viral load are contradictory. Firstly, in vitro data indicate very strong virucidal effects that are not replicated in clinical studies. Secondly, most clinical studies identify a limited effect, do not include a control/placebo group, or do not evaluate viral viability in an infection model. In the current manuscript, we perform a double-blind, randomized clinical trial where salivary viral load was measured before and after the mouthwash, and where saliva samples were also cultured in an in vitro infection model of SARS-CoV-2 to evaluate the effect of mouthwashes on viral viability. Our data show a 90–99% reduction in SARS-CoV-2 salivary copies with one of the tested mouthwashes, although we show that the remaining viruses are mostly viable. In addition, our data suggest that the active ingredient concentration and the overall excipients’ formulation can play an important role; and most importantly, they indicate that the effect is not immediate, being significant at 15 min and having maximum effectiveness after 1 h. Thus, we show that some oral mouthwashes can be useful in reducing viral transmission, although their efficacy must be improved through refined formulations or revised protocols.