Last updated: August 19, 2020
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The following is a curated review of key information and literature about this topic. It is not comprehensive of all data related to this subject.
Use of masks and face coverings by the general public is an important mitigation strategy to reduce transmission of SARS-CoV-2. As the pandemic has progressed, evidence for the use of masks has strengthened.
The rate of asymptomatic COVID-19 disease is high, and asymptomatic and presymptomatic transmission is known to occur (Moriarty, March 2020; Kimball, April 2020; Wei, April 2020; He, April 2020). Therefore, symptom monitoring alone is not adequate to prevent transmission. Mask use, in conjunction with other mitigation measures, is recommended by the CDC because it may be the primary way to halt transmission.
Masking may also reduce viral inoculum when transmission occurs, resulting in more mild disease (Gandhi, July 2020). Current data on mask use to prevent SARS-CoV-2 transmission is limited to observational studies and extrapolation of data about other respiratory viruses, but randomized controlled trial data is forthcoming.
Here we describe data on the use of masks to prevent transmission of SARS-CoV-2 in the community; for information on transmission prevention in the healthcare setting, including a discussion of the potential routes of SARS-CoV-2 transmission, please see the Personal Protective Equipment in Medical Settings Section.
Association Between Universal Masking in a Health Care System and SARS-CoV-2 Positivity Among Health Care Workers (Wang, July 2020)
- After a universal hospital masking policy for all healthcare workers and patients, the proportion of symptomatic healthcare workers with positive test results for SARS-CoV-2 declined from 14.7% to 11.5%.
- This decline occurred despite rising case numbers in the state.
Physical distancing, face masks, and eye protection to prevent person-to-person transmission of SARS-CoV-2 and COVID-19: a systematic review and meta-analysis (Chu, June 2020)
- In a systematic review and meta-analysis of 172 observational studies in healthcare and non-healthcare settings of > 20,000 patients with COVID-19, MERS, or SARS who did not use any mitigation measures, the risk of virus transmission was 17.4%.
- The addition of a mask or respirator decreased the transmission risk to 3.1%.
- There was a stronger association of protection with N95 or similar respirators as compared to disposable surgical masks or similar reusable 12–16-layer cotton masks.
- The primary studies on face masks in this meta-analysis had low-certainty evidence.
Community Use Of Face Masks And COVID-19: Evidence From A Natural Experiment Of State Mandates In The US (Lyu, June 2020)
- An assessment of statewide mask mandates’ effect in 15 states found that mask mandates reduced COVID-19 growth by 1-2% per day.
- Overall, an estimated 230,000-450,000 cases were averted by state mask mandates.
Absence of Apparent Transmission of SARS-CoV-2 from Two Stylists After Exposure at a Hair Salon with a Universal Face Covering Policy (Hendrix, May 2020)
- Two hair stylists in Missouri who wore masks throughout their time working served 139 clients prior to being diagnosed with COVID-19.
- Of 104 clients who were interviewed, 98% wore masks for the entire appointment.
- No symptoms of COVID-19 were identified among the exposed clients or their secondary contacts.
- Two randomized controlled trials are ongoing to better assess the optimal use of face masks for COVID-19 - Medical Masks vs N95 Respirators for COVID-19 (n=576) and Reduction in COVID-19 Infection Using Surgical Facial Masks Outside the Healthcare System (n=6000).
Overall, based on observational studies, masks appear to be effective in reducing transmission of SARS-CoV-2. Randomized controlled trial data is forthcoming.