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Can N95 Masks Be Reused?

n95 masks protecting against COVID-19 virus

With recent PPE shortages for healthcare workers, researchers have begun to investigate the efficacy of decontaminating N95 respirators as a means of maintaining the supply during the COVID-19 pandemic. Factors considered for the effective reuse of these masks are fit, filter efficiency, and decontamination/disinfection level both for SARS‐CoV‐2 (i.e., the causative virus for COVID‐19), and other organisms of concern in a hospital environment.

The U.S. Food and Drug Administration (FDA) recommends 6‐log10 reduction in either the most resistant bacterial spores for the system or in a mycobacterium species to authorize the use of a decontamination method of N95 respirators for single or multiple uses. While the goal is primarily inactivation against SARS‐CoV‐2, testing of decontamination methods against the virus may not always be available. For decontamination methods considered for single use, the recommendation is a 6‐log10 reduction in the infective virus concentration of three non‐enveloped viruses.

Vaporized Hydrogen Peroxide (VHP) Method

Based on these recommendations, Charles River’s Viral Clearance team collaborated with investigators at Mass General Hospital and Harvard University to explore the efficacy of VHP treatment of N95 respirators against surrogate viruses covering a wide range of disinfection resistance for emergency decontamination and reuse of PPE.

  • Read more about the study

    In this study, one cycle of VHP sterilization was found to be effective in the inactivation of five viruses with varying resistance to disinfection. The surrogate viruses used in this study included:

    • Influenza A (InfA)
    • Bovine viral diarrhea virus (BVDV)
    • Herpes simplex virus (HSV)
    • Feline calicivirus (FCV)
    • Porcine parvovirus (PPV)

    In general, DNA viruses are more resistant to disinfection than RNA viruses, non-enveloped viruses are more resistant than enveloped viruses, and smaller size-viruses are more resistant than larger-size viruses. Thus, the five viruses selected represent a spectrum of resistance to disinfection. The highest concentration that can be obtained before decontamination is usually dependent on the stock solution's concentration of the tested virus and on the persistence of the virus on the given surface.

    VHP decontamination of respirator surfaces spiked with PPV (single-stranded, non-enveloped DNA, small virus (18‐24 nm)) was reliably quantified due to

    • High initial stock concentration and sustained concentration of infective units of PPV on surfaces
    • High persistent concentration of infective units of PPV on the surfaces for a prolonged period of hold time (which the same amount of time that the virus spends on the surface without the decontamination procedure)
    • The detection of live infective units in culture after decontamination

    VHP decontamination of respirator surfaces spiked with PPV ranged from 5.61 to 7.02 log10 reduction, showing a high level of disinfection/inactivation against this non‐enveloped virus.

Moist Heat Method

Center for Disease Control and Prevention (CDC) guidance on the decontamination and reuse of N95s also recommends the use of moist heat (60°C, 80% relative humidity, 15‐30 min) based on literature that showed preservation of fit efficiency and inactivation of H1N1 of spiked masks. The team also explored the efficacy of moist heat under these conditions as a decontamination method for an N95 respirator against various pathogens.

  • Read more about the study

    We tested three viruses using moist heat decontamination:

    • Influenza A (InfA)
    • BVDV
    • PPV

    While moist heat decontamination has been shown previously to preserve fit and filter efficiency for N95 respirators, results were less promising for decontamination. Our study revealed limitations of the efficacy of moist heat decontamination against the selected pathogens. The method’s efficacy viruses varied greatly; it was effective against InfA, modestly effective against BVDV, and not effective at all against PPV.

    In and of itself, decontamination of N95s is possible; however, it is important to consider the additional factors when evaluating the merits of different decontamination methods:

    • The number of possible decontamination cycles before the fit deteriorates
    • Filter efficiency
    • Use patterns of the respirators in between decontamination treatments
    • Whether the respirators are returned to the original users after decontamination

    These factors may affect the performance and the risk of failure of these decontaminated respirators and compromise the efficacy of bioburden reduction. There is little information on the effect of multiple decontamination cycles using moist heat decontamination under these conditions, but a recent non‐peer reviewed study suggests that the filter efficiency may be maintained up to 20 cycles.

The Results

Although alternative decontamination techniques continue to be evaluated, of the two models outlined above, our results concluded that VHP is a more effective approach based on the study conditions chosen by MGH.

Contact us to learn more about these studies or our viral clearance program.

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