Top 5 Takeaways

1. Consistent Mask Use Reduces Infection Risk: Consistently wearing a face mask or respirator in indoor public settings was associated with lower odds of testing positive for SARS-CoV-2.
2. Respirators Offer Highest Protection: N95/KN95 respirators provided the most significant protection compared to no mask use, with an adjusted odds ratio (aOR) of 0.17.
3. Surgical Masks Also Effective: Wearing surgical masks was associated with lower odds of a positive test result (aOR = 0.34) compared to no mask use.
4. Cloth Masks Less Effective: Cloth masks showed a reduction in infection odds (aOR = 0.44) but were not statistically significant.
5. Importance of Consistency: The study emphasized that the most critical factor is consistently wearing a comfortable, well-fitting mask or respirator.

Original Article Author and Citation

Corresponding Author

Seema Jain, Seema.Jain@cdph.ca.gov

Kristin L. Andrejko, Kristin.Andrejko@cdph.ca.gov

Suggested Citation

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.mm7106e1

Summary

This study assessed the real-world effectiveness of face masks and respirators in preventing SARS-CoV-2 infection among California residents from February to December 2021. The findings indicated that consistent use of face masks or respirators in indoor public settings significantly reduced the odds of testing positive for SARS-CoV-2. N95/KN95 respirators provided the highest level of protection, followed by surgical masks. Cloth masks were less effective and not statistically significant. The study underscores the importance of wearing a well-fitting and comfortable mask consistently.

Methods

The study used a test-negative case-control design, enrolling California residents who received a positive or negative SARS-CoV-2 test result between February 18 and December 1, 2021. Participants were interviewed via telephone to collect data on mask use, vaccination status, and other sociodemographic characteristics. The primary analysis compared mask use between 652 case-participants (positive test) and 1,176 control-participants (negative test). Adjusted odds ratios were calculated using conditional logistic regression, accounting for various factors including vaccination status and sociodemographic variables.

Discussion

The study found that consistent use of face masks or respirators in indoor public settings significantly reduced the risk of acquiring SARS-CoV-2 infection. N95/KN95 respirators offered the highest level of protection, followed by surgical masks. The findings support existing research on the effectiveness of face masks and respirators in filtering virus-sized particles and reducing community-level transmission. Limitations of the study include reliance on self-reported data and the inability to account for other preventive behaviors or the fit and correctness of mask use.

Conclusion

Consistently wearing a well-fitting face mask or respirator in indoor public settings significantly reduces the risk of SARS-CoV-2 infection. N95/KN95 respirators offer the highest level of protection, but the most important factor is the consistent use of a comfortable and well-fitting mask. These findings reinforce the importance of mask use in addition to being up to date with COVID-19 vaccinations to protect against SARS-CoV-2 infection.

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