Evidence Synthesis Network

Effectiveness, Use and Re-Use of Masks in Hospitals During the Omicron Wave

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Last Updated: January 10, 2022

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This Briefing Note was completed by the Research, Analysis, and Evaluation Branch (Ministry of Health) based on information provided by members of the COVID-19 Evidence Synthesis Network. Please refer to the Methods section for further information.

Purpose

This briefing note summarizes scientific evidence on the filtration performance of masks and their optimal use and re-use in hospital settings in the context of the Omicron variant during the COVID-19 pandemic. It also summarizes jurisdictional best practices for mask use/re-use by hospital staff.

Key Findings

It is important to note that most of the scientific evidence and jurisdictional practices identified in this note was published prior to the emergence of the Omicron variant.

Implications for Ontario

In the context of Omicron, the interim recommended personal protective equipment when providing In the context of Omicron, the interim recommended personal protective equipment when providing direct care for patients with suspect or confirmed COVID-19 includes a fit-tested, seal-checked N95 respirator (or equivalent or greater protection), eye protection, gown, and gloves.

Supporting Evidence

The section below summarizes scientific evidence on the filtration performance of masks and their optimal use and re-use in hospital settings in the context of the Omicron variant during the COVID-19 pandemic (i.e., from November/December 2021). It also includes information on jurisdictional best practices for use (e.g., by activity type), re-use, and reprocessing of N95 masks in hospital settings.

The following limitations should be noted:

  • The scientific evidence searches were limited to systematic reviews, meta-analyses, and reviews. However, some individual studies were included if identified and relevant. Limited information was identified on the topics of interest. 
  • Most of the identified literature focused on COVID-19 variants prior to the emergence Omicron. This literature was included because there may be applicable lessons learned. It will be stated explicitly when Omicron-specific results are discussed.
  • The methodological quality of some of the identified literature was rated using AMSTAR by McMaster Health Forum. These ratings are available here. The methodological quality of all other sources identified is unclear as they have not been assessed as the Research, Analysis, and Evaluation Branch, which does not have the expertise to make such assessments. 

Scientific Evidence

  • Mask Filtration Performance: One systematic review and two single studies found that N95 masks (or their equivalent) have the best filtration performance. A high-quality systematic review (February 2021, pre-print) compared the filtration performance of four different types of masks (i.e., N95 respirators, surgical masks, medical masks, and non-medical masks). The review indicated that N95 or equivalent (e.g., FFP2 and KN95) masks should be the primary choice whenever possible, whether in health care or community settings. However, the review did not analyze findings for N95 and KN95 masks separately.
  • Mask Fit: Based on the evidence, it is important to select a mask that optimizes fit (e.g., in relation to facial hair) and performance with the N95 mask providing the best filtration.
    • Three highly relevant rapid reviews of low- and medium-quality focused on filtration performance of KN95 masks compared to surgical masks or N95 masks, factors affecting the performance of KN95 masks, and/or approaches to improving the fit and performance of KN95 masks: 
      • A low-quality rapid review (December 2021) concluded that given the high transmissibility of the Omicron variant and the potential increased contribution of aerosol transmission, it is important for the public to select a mask that optimizes fit and filtration (e.g., non-fit tested N95, KN95, three-layer cloth mask); and
      • A medium-quality review (February 2021) found a significant reduction of adequate fit of KN95 masks as the length of facial hair increased, and a low-quality review (June 2021) found the same and suggested adopting the use of simple resistance exercise bands as an approach to improve the fit of commonly used face masks (including N95, KF94, KN95, and procedure masks).
    • Three single studies also focused on aspects of mask fit:
  • Reprocessing and/or Re-using N95 Masks via Decontamination Methods: Three systematic reviews (quality not assessed) focused on the effectiveness of different decontamination methods for mask re-use in the context of the COVID-19 pandemic, prior to Omicron. For example: 
    • A systematic review (March 2021) found that ultraviolet germicidal irradiation (UVGI), hydrogen peroxide vapour (HPV), moist heat, and microwave-generated steam processing effectively sterilized N95 respirators and retained filtration performance. UVGI and HPV damaged respirators the least. However, more research is needed on decontamination effectiveness for SARS-CoV-2 because few studies specifically examined this pathogen.
    • A systematic review (June 2021) found disinfectant/sterilizing agents most frequently tested at different concentrations and exposure periods were UVGI, HPV, and steam sterilization. The only disinfectants/sterilizers that did not caused degradation of the material-integrity were alcohol, electric cooker, ethylene oxide, and peracetic acid fogging. Exposure to UVGI or microwave-generated steam resulted in a non-significant reduction in filter performance.

International Scan

  • Types of Masks, Use and Fit: Information about jurisdictional practices related to types of mask used in hospital settings and conditions of use including fit was identified in Australia, the United Kingdom (UK), the United States (US), and the World Health Organization (WHO).
    • Australia: The Australian Department of Health (December 9, 2021) recommended that fit checks must be completed by a wearer every time they put on a respirator, and that respirators, including the P2, N95, KN95, and FFP2, need to be tested for particulate filtration to ensure that they filter out a minimum of 94% or 95% solid and liquid aerosols that do not contain oil.
    • UK: The Health Protection Surveillance Centre in the UK recommends that if respirator masks (FFP2s or N95s) are not fluid repellent, additional protection, such as a visor, be used in situations where there is a splash risk. Fit testing is also recommended for all staff and prioritization of health care workers (HCWs) who are most likely to be involved in performing aerosol-generating medical procedures (AGMP). Moreover, based on the RAG (Red, Amber, Green) rating of wards, the Royal College of Physicians of Edinburghrecommends that in green zones (non-COVID-19 area), surgical masks must be worn when within two metres of a patient or in isolation rooms, surgical masks must be worn at all times in amber zones (COVID-19 cases without AGMP being performed), and FFP3 respirators must be worn at all times in red zones (COVID-19 cases with AGMP being performed).
      • In the context of Omicron, UK guidance (December 2021) recommends universal use of face masks (Type II or IIR) for staff and face masks/coverings for all patients/visitors within health and care settings over the winter period (i.e., until at least March/April 2022).
    • US: Similar to the UK, the US Food and Drug Administration (FDA) recommends that if respirator masks (FFP2s or N95s) are not fluid repellent, additional protection, such as a visor, be used in situations where there is a splash risk. Fit testing is also recommended for all staff and prioritization of HCWs who are most likely to be involved in performing AGMP. Other information from the US includes:
      • The US FDA’s Emergency Use Authorization (EUA) authorizes the use of certain National Institute for Occupational Safety and Health (NIOSH)-approved respirator models in health care settings. The EUA is based on findings from NIOSH researchsuggesting that all approved filtering facepiece respirators with exhalation valves, even without covering the valve, performed the same or better than surgical masks, procedure masks, cloth masks, or fabric. The FDA also noted that some N95 respirators are intended for use in a health care setting, specifically single-use, disposable respiratory protective devices used and worn by HCWs during procedures to protect both the patient and health care personnel from the transfer of microorganisms, body fluids, and particulate material. 
      • The NIOSH Certified Equipment List identifies that the elastomeric respirators (equipped with a replaceable particulate filter) without exhalation valves or with filtered exhalation valves may be used in surgical settings. Other powered air purifying respirators (PAPRs) approved by NIOSH should not be used in surgical settings due to concerns that the blower exhaust and exhaled air may contaminate the sterile field. Lastly, in an update to address NIOSH-Approved Air Purifying Respirators for Use in Health Care Settings During Response to the COVID-19 Public Health Emergency, the FDA indicated that facilities using elastomeric respirators and PAPRs should have up-to-date cleaning and disinfection procedures, which are an essential part of use for protection against infectious agents.
      • Pre-Omicron, the Centers for Disease Control and Prevention (CDC; September 2021) advised prioritizing the use of N95 respirators and well-fitting facemasks by activity type when N95 respirators are so limited that routinely practiced standards of care for all HCWs wearing N95 respirators when caring for a patient with SARS-CoV-2 infection are no longer possible. N95 respirators beyond their manufacturer-designated shelf life, when available, are preferable to use of well-fitting facemasks. The use of N95s or elastomeric respirators or PAPRs should be prioritized for HCWs with the highest potential exposures including being present in the room during AGMPs performed on persons with SARS-CoV-2 infection.
    • WHO: According to the WHO (January 2022), in areas of community or cluster transmission, HCWs, caregivers, and visitors should always wear a respirator or mask when in the health facility, even if physical distancing can be maintained. Masks should be worn throughout their shifts, apart from when eating, drinking or needing to change the mask for specific reasons. Health workers and caregivers include doctors, nurses, midwives, medical attendants, cleaners, community health workers, and any others working in clinical areas.
      • In the context of Omicron, the WHO (December 2021) advised that a respirator (FFP2, FFP3, NIOSH-approved N95, or equivalent or higher-level certified respirator) or a medical mask should be worn by HCWs along with other personal protective equipment (PPE) (i.e., a gown, gloves and eye protection) before entering a room where there is a patient with suspected or confirmed COVID-19. Respirators should be worn in the following situations: in care settings where ventilation is known to be poor, cannot be assessed, or the ventilation system is not properly maintained based on HCWs’ values and preferences and on their perception of what offers the highest protection possible to prevent SARS-CoV-2 infection.
  • Mask Re-Use: In September 2020, when P2 and N95 masks were the only particulate filter respirators (PFRs) in compliance with Australian standards, the Infection Control Expert Group in Australia recommended that single-use PFRs can be used for a single session of care lasting up to four hours and that they should be discarded as soon as they are removed, and not stored or decontaminated for re-use. They also recommended that users be instructed in the correct method of fitting, removing, and fit-checking PFRs, as training can improve facial seal achieved.
  • Conditions of Mask Re-Use: Pre-Omicron, the CDC (September 2021) noted that the decision to implement policies that permit extended use of N95 respirators should be made by the professionals who manage the institution’s respiratory protection program, in consultation with their occupational health and infection control departments with input from the state/local public health departments.
    • Extended use is well suited to situations wherein multiple patients with the same infectious disease diagnosis, whose care requires use of a respirator, are cohorted (e.g., housed on the same hospital unit such as a COVID-19 unit). 
      • HCWs can consider using a face shield or surgical facemask over the respirator to reduce contamination of the respirator, especially during AGMPs or procedures that might generate splashes and sprays. It is not known how facemasks placed over the respirator can affect the fit so caution should be used.
    • Limited re-use of N95 respirators: This might become necessary when caring for patients with SARS-CoV-2 infection. However, it is unknown what the potential of contact transmission is for SARS-CoV-2, and caution should be used.
    • Mask Re-Use Storage and Care: One strategy to mitigate the contact transfer of pathogens from the respirator to the wearer could be to issue each HCW who may be exposed to patients with SARS-CoV-2 infection a minimum of five respirators. Each respirator will be used on a particular day and stored in a breathable paper bag until the next week. This will result in each worker requiring a minimum of five N95 respirators if they put on, take off, care for them, and store them properly each day. If this strategy is used, the total number of donnings should still not exceed five times before discarding the respirator, when no manufacturer instructions are provided to indicate otherwise.

Canadian Scan

  • Mask Fit and Filtration: Prior to the emergence of Omicron, the Public Health Agency of Canada (PHAC; last update on November 2021) offers advice for the use of COVID-19 medical masks and respirators, specifically that N95 respirators achieve a minimum particulate filtration efficiency of 95% and that when worn properly, the edges of the mask form a seal around the nose and mouth. Moreover, Health Canada accepts the US NIOSH certification as an appropriate quality standard for N95 respirators, and all certified N95 respirators must have an approval number stamped on the mask, represented as TC-84A-####n. An expired respirator can still be effective at protecting HCWs if it can be fit-tested, the straps are intact, and there are no visible signs of damage. In addition, Health Canada has asked manufacturers and importers to stop the sale of any products that do not meet the filtration criteria of 95% and re-label them as non-medical use face masks, as they could be used in settings where 95% filtration is not needed.
  • Hospital Staff Mask Use: In the context of Omicron, PHAC guidance (December 23, 2021) recommends masking for the full duration of shifts in all health care settings during the COVID-19 pandemic. Depending on community transmission rates, the mask chosen can be a well-fitting medical mask or a respirator. HCWs can choose to wear a respirator at any time taking into account such factors as the community incidence of SARS-CoV-2, patient’s ability to tolerate a mask, patient behaviours such as shouting or heavy breathing, requirement of extensive or prolonged close proximity, and other factors. Employers must ensure that every HCW has access to a respirator, so that they can put it on quickly if the need is identified during the point of care risk assessment. No HCW should be denied a respirator at any time.
    • In the context of Omicron, a technical brief (December 2021) from Public Health Ontario (PHO) noted that for standard care of patients with suspect or confirmed COVID-19, Alberta and BC recommend surgical/procedure (medical) masks, and an N95 respirator (or equivalent or greater protection) is recommended when AGMPs are being performed.
      • PHO also noted that given the undetermined impact of the Omicron variant, the interim recommended PPE when providing direct care for patients with suspect or confirmed COVID-19 includes a fit-tested, seal-checked N95 respirator (or equivalent or greater protection), eye protection, gown, and gloves. Other appropriate PPE includes a well-fitted surgical/procedure (medical) mask, or non-fit tested respirator, eye protection, gown, and gloves for direct care of patients with suspect or confirmed COVID-19. Fit-tested N95 respirators (or equivalent or greater protection) should be used when AGMPs are performed or anticipated to be performed on patients with suspect or confirmed COVID‑19.

Ontario Scan

  • Guidance for Mask Use: In the context of Omicron, a PHO technical brief (December 2021) related to mask use for hospital staff advised:
    • There are early estimates of significant increased transmissibility and decreased vaccine effectiveness with the Omicron variant. It is unclear currently if there is a change in the infectiousness of aerosols as a possible explanation for this increase in transmissibility. Considering this, all layers of protection in health care settings should be optimized to prevent transmission until more information is available.
    • Given the undetermined impact of the Omicron variant, the interim recommended PPE when providing direct care for patients with suspect or confirmed COVID-19 includes a fit-tested, seal-checked N95 respirator (or equivalent or greater protection), eye protection, gown, and gloves. Other appropriate PPE includes a well-fitted surgical/procedure (medical) mask, or non-fit tested respirator, eye protection, gown, and gloves for direct care of patients with suspect or confirmed COVID-19. 
    • Fit tested N95 respirators (or equivalent or greater protection) should be used when AGMPs are performed or anticipated to be performed on patients with suspect or confirmed COVID‑19.
  • Guidance for Mask Decontamination: Although prior to the emergence of Omicron, Ontario Health (April 2020) advised that UVGI and HPV are the most promising decontamination methods, based on available scientific evidence demonstrating their ability to inactivate infectious pathogens and maintain the integrity of the N95 respirator. However, the impact of each method on respirator performance (filtration and fit) is dependent on the respirator model. Those in charge of infection control practices in their jurisdictions should be aware of the N95 respirator models in their facilities and consider the pros and cons of each method when choosing a reprocessing method.

Methods

The COVID-19 Evidence Synthesis Network is comprised of groups specializing in evidence synthesis and knowledge translation. The group has committed to provide their expertise to provide high-quality, relevant, and timely synthesized research evidence about COVID-19 to inform decision makers as the pandemic continues. The following members of the Network provided evidence synthesis products that were used to develop this Evidence Synthesis Briefing Note.