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Effectiveness of standard face masks compared to respirator masks

Author: Dr Andrew Dickson, Occupational Health Physician

Summary of evidence produced by the Centre for Evidence-Based Medicine, University of Oxford in conjunction with Universities of Leicester, Alberta, Toronto and Evidence Synthesis Ireland.

Original document: https://www.cebm.net/wp-content/uploads/2020/03/COVID-CAT-PPE-MASKS-7.pdf

Published by Centre for Evidence-Based Medicine 23 March 2020

Main points:

  • Most of the research comparing ‘masks’ (surgical face masks) and ‘respirators’ (FFP3 or similar) relates to influenza or other relatively benign respiratory conditions.

  • There have been no published trials comparing masks and respirators in the transmission of COVID-19.

  • Current guidance is therefore based partly on indirect evidence – notably, from past influenza, SARS and MERS outbreaks – as well as expert opinion, custom and practice.

  • Official UK guidance (February 2020) that both standard and respirator masks provide 80% protection against SARS-CoV-2 was based largely on trials for seasonal flu – so may or may not apply to COVID-19.

  • For non-aerosol generating procedures (non-AGPs) in clinical care, there is no evidence that respirator masks add value over standard masks when both are used with recommended wider PPE measures.

  • A recent meta-analysis (total of 9171 participants) found no statistically significant difference in the effectiveness of masks versus respirators in transmission of influenza, avian and swine flu viruses.

  • A face mask or respirator worn without additional PPE will be less effective.

  • WHO guidance for all healthcare settings (Author’s note - and thus perhaps transferrable to any close human encounter) recommends:

Triage staff (implicitly, by non-clinical staff without prolonged contact)

Mask                    +   hand hygiene

Suspected or confirmed case of COVID-19 requiring healthcare facility admission and no AGPs

Goggles               +   hand hygiene, mask,

                                   gown, gloves

Suspected or confirmed case of COVID-19 requiring healthcare facility admission and aerosol generating procedures OR collection of specimens for laboratory diagnosis

Goggles               +   hand hygiene,                            

                                   respirator, gown,

                                   gloves

Practical implications for the workplace

Author’s interpretation

  1. The question of whether face masks or other PPE should be worn by individuals maintaining a distance of at least 2 metres is not addressed here

  2. Duties requiring close contact with others (staff for the public): surgical mask recommended. [This would be in line with WHO recommendations for health triage staff. What constitutes close contact is not defined though perhaps within 2 metres].

  3. Staff having close contact with individuals with COVID-19-type symptoms should wear a respirator mask in addition to a gown, goggles and gloves.

  4. Where individuals are likely to be aerosolising from the mouth or nose (e.g. coughing or splitting, perhaps shouting) and have COVID-19-type symptoms wear an FFP3-type respirator in addition to gown, goggles and gloves. The same for individuals taking swabs or other samples for laboratory diagnosis.