Research and analysis

The role of face coverings in mitigating the transmission of SARS-CoV-2 virus: statement from the Respiratory Evidence Panel (2021)

Updated 30 March 2023

Background

Public Health England (PHE) convened an expert Respiratory Evidence Panel in February 2021 to critically assess the evidence behind SARS-CoV-2 transmission to inform their guidance and recommendations.

The panel comprised a group of infectious disease, hygiene, virology, microbiology, respiratory infection, engineering, occupational safety, and infection prevention and control (IPC) experts, including representation on relevant UK advisory panels (Scientific Advisory Group for Emergencies (SAGE) and New and Emerging Respiratory Virus Threats Advisory Group (NERVTAG).

Nominated individuals participated from UK-wide professional infection societies (British Infection Association, Infection Prevention Society, Healthcare Infection Society, Clinical Virology Network) and the airborne High Consequence Infectious Diseases network, with international participants recommended by the Health and Safety Executive (from the Partnership in European Research in Occupational Safety and Health and the Sheffield Group). Find out more about the list of participants and participants interests.

PHE’s COVID-19 Rapid Evidence Service provided an overview of review-level evidence (searches up to 28 April 2021), refined with input from the panel, and with relevant information extracted and presented.

The key findings below are taken from this synthesis: The role of face coverings in mitigating the transmission of COVID-19: an overview of evidence. Key findings were given a confidence rating (low, medium and high confidence) through combining this overview of evidence with expert knowledge and experience.

The panel met 3 times on 1 March 2021, 21 April 2021 and 12 May 2021.

Key findings and recommendations

The panel assessed review-level evidence (searches up to 28 April 2021) to consider the potential effectiveness of face coverings in mitigating transmission of SARS-CoV-2, including consideration of:

• the role of airborne transmission in relation to SARS-CoV-2
• the transmissibility of new SARS-CoV-2 variants
• the effectiveness of face coverings (including efficacy of different types of face coverings and respirators and factors that may impact on this) ^{[footnote 1]}

The panel concluded that:

• airborne transmission beyond 2 metres is possible and that contributory factors to airborne transmission of SARS-CoV-2 include poorly ventilated indoor settings, prolonged exposure and activities that may generate more aerosols (high confidence)
• individual characteristics likely to increase the risk of transmission include high viral load and early symptomatic disease (medium confidence)
• effective ventilation as part of the implementation of the hierarchy of risk controls should be used to reduce airborne exposures beyond 2 metres (high confidence) ^{[footnote 2]}
• certain variants of concern (VOCs) are likely to have increased transmissibility, although the magnitude of reported increase varies by geographic region, modelling approach, relative transmissibility of concurrent circulating strains and current control measures in place (medium confidence – Alpha (B.1.1.7) variant, low confidence – Beta (B.1.351) and Gamma (P.1) variants, not considered (given timing of evidence reviewed) – Delta (B.1617.2 variant)
• the biological mechanism of the increase in transmissibility of VOCs is not yet clear, though for Alpha (B.1.1.7) increased transmissibility is likely to be due to either increased viral load (inferred from lower Ct values) or altered dose-response relationship (low confidence)
• the evidence to date suggests that the modes of transmission of VOCs has not changed compared to other variants, so it is expected that the same infection prevention and control measures should be appropriate, including ventilation, hand hygiene, face coverings and, in high risk settings, respiratory personal protective equipment PPE (medium confidence)
• the evidence suggests that all types of face coverings are, to some extent, effective in reducing transmission of SARS-CoV-2 in both healthcare and public, community settings – this is through a combination of source control and protection to the wearer (high confidence)
• laboratory data shows that non-medical masks (such as cloth masks) made of 2 or 3 layers may have similar filtration efficiency to surgical masks (high confidence)
• epidemiological evidence (usually of low or very low certainty) from SARS-CoV-2 and other respiratory viruses suggests that, in healthcare settings, N95 respirators (or equivalent) may be more effective than surgical masks in reducing the risk of infection in the mask wearer ^{[footnote 3]} (low confidence)
• evidence, mainly from laboratory studies, suggests that face coverings should be well-fitted and cover the mouth and nose to increase effectiveness (as fit is a limiting factor in the overall mask protective efficiency independently of the filtration efficiency of its fabric) (high confidence)
• there is a need for improved training (in health and care settings) and public health messaging (in community settings) on mask fitting (and quality in the community) (medium confidence)
• there is insufficient evidence to support the use of double-masking in a healthcare setting (not ranked due to insufficient evidence)

1. Studies were limited to those on SARS-CoV-2, except relevant reviews and meta-analyses that additionally included other respiratory viruses. ↩

2. Based on panel’s expert knowledge and experience (effectiveness of ventilation was not assessed as part of the evidence review). ↩

3. However, settings and care interactions are often poorly described in the literature, or include high risk areas within healthcare settings with frequent aerosol generating procedures (AGPs); evidence in specific care areas is lacking. The evidence assessed referred to ‘N95 respirators’ or ‘N95 respirators and equivalent’; in the UK, if risk assessment deems that respiratory protective equipment is needed, the Health and Safety Executive (HSE) advises as a minimum, this should be a FFP3 respirator. ↩