Investigating the effectiveness of commercially available mouthwash on SARS-CoV-2 in vivo using viable virus titre as the primary outcome. A randomised controlled trial
Authors: Seymour D.W. , Forshaw G. , Porteous M. , Mawer D. , Wiggins F. , Mitchell A. , Hewitt C. , Beetar-King T. , Davies K.A. , Jackson D. , Hannah M.J. , Pitcher M. , Arnold U. , Strachan R. , Killip M.J. , Nixon P.J. 
Published: July 2024

This multi-arm, parallel group, single-blinded randomised controlled trial aimed to assess three commercially available mouthwashes effectiveness against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). This manuscript has been written in accordance with the CONSORT statement.

Methods. Eligible participants were SARS-CoV-2 positive with a positive test in the last 72 h. All participants had mild to moderate symptoms and could provide five saliva samples over a 60 min period. Participants delivered a baseline saliva sample and then used a mouthwash as per manufacturer’s instructions. They provided further saliva samples at minute 1, 10, 30 and 60. Participants were randomised to one of four groups; OraWize+, Total Care Listerine, Cool Mint Listerine and water (control). The lab-based research team were blind to the intervention. The research question was: can SARS-CoV-2 be rendered inactive in saliva by using a mouthwash and how long does this effect last? The primary outcome was the amount of viable infectious SARS-CoV-2 virus in the sample, compared to the baseline sample. The secondary outcome measure was the amount of genetic material from the SARS-CoV-2 virus in the sample, measured via PCR testing.

Results. In total 100 participants were recruited (25 per group). Eight participants did not receive the allocated intervention and did not have saliva samples collected. There were no adverse events. In total 42 of the 92 participants had viable virus which could be cultured at baseline. Statistical analysis of the primary outcome was not advised due to the reduced level of viable virus at baseline and the positive skewness present in the distribution of log10(titre) data. Observational data of the primary outcome measure is presented.
Analysis of the secondary outcome PCR measure showed that there was strong evidence for a decrease in SARS-CoV-2 RNA levels compared to water for all mouthwashes after 1 min, OraWize+ −0.49 (−0.92, –0.05), p-value 0.029, Cool Mint Listerine −0.81 (−1.25, –0.38), p-value<0.001, Total Care Listerine −1.05 (−1.48, –0.62), p-value<0.001. For the remaining timepoints there was generally no evidence of virus level reduction compared to water although there is weak evidence for a decrease at ten minutes using Total Care Listerine −0.44 (−0.88, 0.01), p-value 0.053.

Conclusion. The three mouthwashes included in this trial observationally demonstrated a reduction in virus titre level 1 min after use, with virus levels normalising up to 60 min compared to the control. Although an interesting observation, this result could not be statistically analysed. Using the secondary outcome PCR measure all three included mouthwashes reduced virus levels compared to water at 1 min and these results were statistically significant. Clinically this result does not support the use of the included mouthwashes to reduce SARS-CoV-2 levels in saliva.