Is one-way masking effective?

With the federal mask mandate for airplanes, airports and public transport abruptly ending last week, the question of “is one-way masking effective?” arises. One-way masking is when one individual is masked yet others are not. Many may find themselves in this situation while the justice department appeals the decision. While the data is clear that masking is most effective when everyone partakes (as discussed in my previous post), there is still some benefit to masking even if those around you are not masked. The degree of effectiveness however depends on what kind of mask the wearer is wearing, the ventilation and air filtration in the space being occupied, physical distancing, the community transmission levels in the area one is traveling from or traveling to, duration of exposure etc.

I previously discussed the best masks to protect against highly transmissible variants such as omicron, which are also the best masks to wear if those around you are not masked. NIOSH-certified N95 masks are still the most effective, but the masks discussed here including KF94s and KN95s are great alternatives if one is unable to get an NIOSH-certified N95. Earlier this year a study showed that consistent use of a face mask indoors was associated with lower chance of becoming infected with SAR-COV2 and respirators with the highest filtration capacity offered the most protection. The details of this study were discussed in my previous post.

Studies have shown that wearing an N95, KN95 or KF94 can reduce risk of transmission to 1% over one hour of exposure if everyone is wearing one, but there is still benefit to wearing one even if others are not. If you are the only one masking and you opt to wear a well-fitted N95, risk of transmission from someone who is infected and unmasked is decreased to 20% over the course of a one hour exposure. This same study found that if the masked person is wearing a surgical mask however, there is a 90% risk of being infected after 30 minutes of being 5 feet apart. The evidence is again clear that the type of mask and the fit of the mask matters.

Despite the recent ruling ending the mandate, I hope to see the majority of people continuing to mask on planes/public transportation and other crowded areas. I know I will continue to mask to protect the most vulnerable including children who cannot be vaccinated (anyone under age 5) and immunocompromised individuals who don’t receive the full benefit of protection from vaccination alone. Other things to consider are masking will prevent travel disruptions due to getting sick, decrease staff shortages on flights and other modes of transportation (we are already seeing more flight cancellations due to COVID-19 in employees), and will further protect YOU.

Andrejko KL, Pry JM, Myers JF, et al. Effectiveness of Face Mask or Respirator Use in Indoor Public Settings for Prevention of SARS-CoV-2 Infection — California, February–December 2021. MMWR Morb Mortal Wkly Rep 2022;71:212–216. DOI: http://dx.doi.org/10.15585/mmwr.mm7106e1external icon.

Bagheri G, Thiede B, Hejazi B, et al. An upper bound on one-to-one exposure to infectious human respiratory particles. PNAS. 118(49). December 2, 2021. https://doi.org/10.1073/pnas.2110117118

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Lindsley WG, Blachere FM, Beezhold DH, et al. A comparison of performance metrics for cloth masks as source control devices for simulated cough and exhalation aerosols. Aerosol Sci Technol 2021 Oct 3;55(10):1125-42