The efficacy, effectiveness and safety of SARS-CoV-2 disinfection methods (including ozone machines) in educational settings for children and young people
Authors: Edwards Deborah , Csontos Judit , Gillen Elizabeth , Lewis Ruth , Cooper Alison , Gal Micaela , Law Rebecca-Jane , Edwards Adrian 
Published: February 2022

While evidence for the importance of transmission of SARS-CoV-2 from contaminated surfaces is limited, ozone disinfection methods have been considered for surface cleaning as a response to stopping the spread of the virus in educational settings. This rapid evidence summary aimed to search the available literature and summarise findings on the surface survival of SARS-CoV-2, efficacy and effectiveness of ozone machines against SARS-CoV-2, and benefits and harms caused by using these cleaning technologies, including their impact on health. Alternative cleaning technologies, such as light-based technologies and hydrogen peroxide vapour, were also investigated. Findings indicate that gaseous ozone can inactivate different bacteria and viruses, although there is a lack of direct evidence investigating the effect of these cleaning methods on SARS-CoV-2 in real-world settings, specifically in schools. However, regarding harm, ozone is a highly reactive oxidising agent, and high concentrations can contribute to decay of building materials, and health issues (mainly respiratory) by direct exposure or by-product formation. Therefore, leading environmental health organisations do not recommend the use of ozone cleaning technologies in real-world settings, such as schools. Research and policy focus may need to shift towards other interventions that could help reduce transmission, and consequently minimise disruption to education.

Funding statement

The Wales Centre for Evidence Based Care was funded for this work by the Wales Covid-19 Evidence Centre, itself funded by Health & Care Research Wales on behalf of Welsh Government.

TOPLINE SUMMARY

What is a Rapid Evidence Summary?

This Rapid Evidence Summary was completed in two weeks to inform policy- decision making. It is based on a systematic search of the literature, conducted in September 2021. Priority is given to studies representing robust evidence synthesis. No quality appraisal or evidence synthesis are conducted, and the summary should be interpreted with caution.

Background / Aim of Rapid Evidence Summary

Several non-touch disinfectant methods including ozone, light-based technologies, and hydrogen peroxide are being considered to reduce the risk of SARS-CoV-2 virus transmission to children and young people in educational settings. Concerns have been raised about the evidence of efficacy, effectiveness and safety of these technologies in these settings. We aimed to address the following research questions:

What is the evidence for the surface survival of SARS-CoV-2?

What is the evidence for the efficacy (in vitro) and real-life effectiveness (in situ) of ozone machines, light-based technologies and hydrogen peroxide vapour as air or surface disinfectants against SARS-CoV-2?

What are the potential health effects of ozone, in particular for children and young people and the benefits and harms of using ozone machines?

Key Findings

Extent of the evidence base

A total of 82 tertiary, secondary and primary evidence sources was included

Recency of the evidence base

Most studies were published 2020-21, indirect evidence was included from earlier work from 2006 onwards

Summary of findings

SARS-CoV-2 fragments can be found on surfaces up to seven days later in the community but there is a lack of evidence whether these are viable

When accounting for both surface survival data and real-world transmission factors, the risk of surface transmission after a person with COVID-19 has been in an indoor space is minor after 72 hours, regardless of last clean

There is evidence from experimental settings that ozone machines, light-based technologies and hydrogen peroxide do inactivate coronaviruses, including SARS-CoV-2

There is a lack of evidence for the effectiveness of ozone machines, light- based technologies and hydrogen peroxide in real-world settings

There are uncertainties about training requirements for staff, methods for assurance of ozone removal and monitoring of occupational exposure

There is strong evidence of a causal relationship between short term ozone exposure and respiratory health issues; these can occur at very low concentrations of ozone; children with asthma are more at risk

Rooms using ozone machines need to be sealed off to avoid leakage of the ozone gas which is toxic at high concentrations

Ozone may react with materials in the room to form secondary pollutants (e.g. formaldehyde)

The best quality evidence

The US EPA 2021 does not recommend ozone for air cleaning and the UK SAGE EMG 2020a does not recommend technologies that “may generate undesirable secondary chemical products that could lead to health effects such as respiratory or skin irritation (medium confidence). These devices are therefore not recommended unless their safety and efficacy can be unequivocally and scientifically demonstrated by relevant test data” (SAGE EMG 2020a).

Policy implications

There is no direct evidence for the effectiveness and safety of using ozone machines to deactivate SARS-CoV-2 in real-world educational settings for children, young people and staff

There is evidence for the risk of potential harm to children and young people of ozone machines from either ozone or secondary pollutants, in particular but not only, if used in uncontrolled ways in educational settings

Strength of Evidence to date

moderate evidence for the surface survival of SARS-CoV-2

strong evidence of causal relationship between short term ozone exposure and respiratory health issues