Morbidity and Mortality Weekly Report384 MMWR / March 11, 2022 / Vol. 71 / No. 10US Department of Health and Human Services/Centers for Disease Control and Prevention SARS-CoV-2 Incidence in K–12 School Districts with Mask-Required Versus Mask-Optional Policies — Arkansas, August–October 2021
Masks are effective at limiting transmission of SARS-CoV-2,
the virus that causes COVID-19 (1), but the impact of poli-
cies requiring masks in school settings has not been widely
evaluated (2–4). During fall 2021, some school districts in
Arkansas implemented policies requiring masks for students
in kindergarten through grade 12 (K–12). To identify any
association between mask policies and COVID-19 incidence,
weekly school-associated COVID-19 incidence in school
districts with full or partial mask requirements was compared
with incidence in districts without mask requirements during
August 23–October 16, 2021. Three analyses were performed:
1) incidence rate ratios (IRRs) were calculated comparing
districts with full mask requirements (universal mask require-
ment for all students and staff members) or partial mask
requirements (e.g., masks required in certain settings, among
certain populations, or if specific criteria could not be met)
with school districts with no mask requirement; 2) ratios of
observed-to-expected numbers of cases, by district were calcu-
lated; and 3) incidence in districts that switched from no mask
requirement to any mask requirement were compared before
and after implementation of the mask policy. Mean weekly
district-level attack rates were 92–359 per 100,000 persons in
the community* and 137–745 per 100,000 among students
and staff members; mean student and staff member vaccination
coverage ranged from 13.5% to 18.6%. Multivariable adjusted
IRRs, which included adjustment for vaccination coverage,
indicated that districts with full mask requirements had 23%
lower COVID-19 incidence among students and staff members
compared with school districts with no mask requirements.