Can ozone inactivate SARS-CoV-2 A review of mechanisms and performance on viruses

Background

Ozone gas has long been used as a disinfectant for water, air and surfaces because of its strong oxidising power. When the COVID-19 pandemic began, researchers urgently needed to know whether the same oxidising action would work against SARS-CoV-2, the virus that causes COVID-19, and how it compared with ozone's known effects on other viruses. This review set out to bring together the scattered evidence on how ozone inactivates viruses and how well it performs in practice, including the small number of studies that had tested it directly against SARS-CoV-2.

Study design

The authors, based at the University of Barcelona, conducted a literature review of published studies on ozone disinfection of viruses in gas (airborne) and aqueous (waterborne) environments. They compiled data from studies covering 29 different viruses, examining the ozone concentrations used, exposure times, and the resulting reduction in viable virus particles, measured on a logarithmic (log10) scale. The review also examined the proposed biological mechanisms behind ozone's virucidal action, such as damage to the lipid envelope, surface proteins and genetic material of viruses.

Findings

Across the studies reviewed, gas-phase ozone successfully inactivated 28 of the 29 viruses tested, achieving reductions greater than 3 log10 (more than 99.9 percent). Two of the studies included had tested ozone gas directly against SARS-CoV-2 and reported effective inactivation. Airborne viruses were shown to be disinfected at comparatively low ozone concentrations, with 3 to 4 log10 reductions achieved using concentration-time products of around 0.1 to 0.4 mg per litre per minute. The proposed mechanism is that ozone oxidises the lipid envelope and the spike proteins viruses use to enter host cells, and can also degrade the viral genome, though the relative importance of each pathway varied between the studies reviewed.

What the authors concluded

The authors concluded that the existing evidence supports ozone gas as an effective disinfectant against SARS-CoV-2 and a broad range of other viruses, particularly for airborne and surface disinfection at relatively low concentrations. They suggested this made ozone a promising tool for disinfection applications, while noting that its effectiveness depends on factors such as concentration, exposure time, humidity and the surface or medium being treated.

Limitations of this study

This is a review of previously published research rather than new laboratory experiments, so its conclusions are only as reliable as the individual studies it draws on, which used differing test conditions, ozone delivery methods and measurement techniques that are not always directly comparable. Only two of the studies reviewed tested SARS-CoV-2 itself; the rest used other viruses or surrogate organisms as stand-ins, which may not behave identically. The review also focuses on disinfection performance in controlled conditions and environmental settings, not on ozone's effects when used therapeutically inside the human body, so its findings should not be extended beyond surface, air and water disinfection contexts.