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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

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), %
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)
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
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