Can mouthwash cut COVID-19 salivary viral load?

In COVID-19 patients who had mild or no symptoms, the use of 0.05% cetylpyridinium chloride (CPC) and 0.01% on-demand aqueous chlorine dioxide (ACD) mouthwashes did not lead to a reduction in SARS-CoV-2 salivary viral load.

“[Our results] showed that the use of [both types of mouthwash] was not associated with a change from baseline SARS-CoV-2 salivary viral load compared with placebo,” said the researchers.

The CPC mouthwash was not superior to placebo in terms of changes from baseline salivary cycle threshold values at 30 minutes (difference, 0.640; p=0.543), 2 hours (difference, 1.158; p=0.246), 4 hours (difference, 1.283; p=0.209), 10 hours (difference, 0.304; p=0.775), or 24 hours (difference, 0.782; p=0.438). [BMC Oral Health 2024;doi:10.1186/s12903-024-04246-1]

A similar pattern was observed with the on-demand ACD mouthwash across all timepoints evaluated: 30 minutes (difference, 0.905; p=0.371), 2 hours (difference, 0.709; p=0.483), 4 hours (difference, 0.220; p=0.830), 10 hours (difference, 0.198; p=0.854), or 24 hours (difference, 0.784; p=0.447).

The researchers pointed to several reasons that could explain for the lack of clear differences between study arms. Mouthwash concentration is one; characteristics of emerging SARS-CoV-2 variants is another.

“Viral load may vary with time and our results might change following the availability of further evidence with different concentrations of mouthwash from several brands or manufacturers and the continuous emergence of new SARS-CoV-2 variants,” they added.

Furthermore, sampling methods may have influenced the effects of the mouthwashes. For instance, supervised saliva collection may reduce variability between samples. [Am J Otolaryngol 2022;43:103549; Biomedicines 2023;11:1694]

“[Hence,] accurate evaluation of the efficacy of mouthwashes may require different sampling methods, such as the supervised collection of saliva samples, throat gargle sampling, nasopharyngeal swabs, and oropharyngeal swabs with multiple tests,” the researchers explained.

Ninety participants (median age at study entry 33.1 years, 56.7 percent men) were randomized 1:1:1 to use a mouth rinse consisting of 20 mL of 0.05% CPC for 30 seconds, 10 mL of 0.01% on-demand ACD for 1 minute, or 20 mL of purified water (placebo) for a minute.

On-demand ACD

Of note, on-demand ACD was developed only recently to overcome the limitations of ordinary CD for human consumption. [BPB Rep 2020;3:174-178; BPB Rep 2021;4:78-84] “On-demand ACD generates free radicals by catalytic action only when exposed to viruses or live bacteria in the respiratory system, and then exerts strong microbicidal activity. It has been suggested that [this solution] may have potential as a disinfectant mouthwash,” the researchers said.

However, the efficacy of on-demand ACD mouthwash against COVID-19 has not been thoroughly evaluated. “Thus, further evaluation of this agent might lead to it being assigned a role in decreasing the salivary viral load of SARS-CoV-2,” they said.

Practical implications

Although the study suggests the lack of benefit with mouthwashes in reducing or preventing COVID-19 infection in asymptomatic or mildly symptomatic individuals, it does not negate some potential practical implications, the researchers noted.

“Antiviral drugs and vaccines may be insufficient to prevent the spread of COVID-19 infection, and public health services may need to prepare for COVID-19 infection through the implementation of a range of non-pharmaceutical preventive interventions,” they said. “Mouthwashes are cheap, simple to use, and commonly employed as a daily antisep­tic complement to brushing teeth for oral hygiene maintenance.”

Further studies are thus imperative to ascertain the role of mouthwash in the fight against COVID-19. “[U]nderstanding the effects of physical interventions such as mouthwashes is important for planning public health policies for COVID-19,” they said.