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Disclaimer: Early release articles are not considered as final versions. Any changes will be reflected in the online version in the month the article is officially released.

Volume 28, Number 1—January 2022
Research

Mask Effectiveness for Preventing Secondary Cases of COVID-19, Johnson County, Iowa, USA

Jacob RileyComments to Author , Jamie M. Huntley, Jennifer A. Miller, Amelia L.B. Slaichert, and Grant D. Brown
Author affiliations: Johnson County Public Health, Iowa City, Iowa, USA (J. Riley, J.M. Huntley, J.A. Miller, A.L.B. Slaichert); University of Iowa, Iowa City, Iowa, USA (G.D. Brown)

Main Article

Table 1

Mask effectiveness for preventing secondary cases of coronavirus disease, Johnson County, Iowa, USA

Mask use, case-patient/contact Negative Positive Secondary attack rate (95% CI), %
Overall
768
198
20.5 (18.1– 23.2)
Total unmasked* 439 151 25.6 (22.3–29.4)
Unmasked/unmasked 364 131 26.4 (22.9– 30.7)
Unmasked/masked 36 4 10.0 (4.0– 25.3)
Masked/unmasked 39 16 29.1 (19.3–43.9)
Masked/masked 329 47 12.5 (9.6–16.3)
Unknown
69
23
25 (17.5–35.6)
School-age, 5–18 y
Unmasked* 156 53 25.2 (20.1–32.0)
Masked/masked 191 26 12.0 (8.4–17.2)

*When >1 person was unmasked during exposure.

Main Article

Page created: October 12, 2021
Page updated: October 12, 2021
Page reviewed: October 12, 2021
The conclusions, findings, and opinions expressed by authors contributing to this journal do not necessarily reflect the official position of the U.S. Department of Health and Human Services, the Public Health Service, the Centers for Disease Control and Prevention, or the authors' affiliated institutions. Use of trade names is for identification only and does not imply endorsement by any of the groups named above.
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