The recent article by Boutzoukas et al1  analyzed the association of universal vs partial vs optional school masking policies with secondary in-school infection and found an unexpectedly strong association between masking policies and secondary infections given recent studies.2,3  Unfortunately, it appears the authors have failed to consider at least 1 critically important confounding variable. The Centers for Disease Control and Prevention (CDC)4  state that “the close contact definition excludes students who were between 3 to 6 feet of an infected student if both the infected student and the exposed student(s) correctly and consistently wore well-fitting masks the entire time.” We are aware of numerous districts across the country where contact tracing during the period of the study1  would not have correctly identified coronavirus disease 2019 cases truly transmitted in the school to have come from the school because a masked student transmitting to another masked student would not have been considered a close contact according to CDC policy. This would lead to in-school transmission cases in districts with mask mandates being overlooked by contact tracers and incorrectly considered community transmission, giving falsely low rates of secondary transmission in districts with mask requirements. Potentially related, Boutzoukas et al1  found unexpectedly higher rates of primary infections (or community transmission) in the universal vs optional masking districts (125.6/1000 vs 38.9/1000), which could at least partially be due to the close contact policy mentioned previously; if secondary infections were systematically and inappropriately considered primary infections in mask-mandate districts, this would have led to secondary infections being misclassified as primary infections coming from the community. This would have increased primary infection rates while lowering secondary infection rates in universal masking districts. The association observed by Boutzoukas et al1  between masking and secondary transmission may alone have been attributable to different contact tracing policies and not because of masks at all. We worry that a policy that does not consider masked transmission in schools makes the study a self-fulfilling prophecy: the expected result is lower identified secondary transmission rates in masking districts simply because of this policy. If contact tracers discount the possibility of in-school transmission because a student was masked, as the CDC instructs, even if this only occurs in some schools, that would be sufficient to cloud the entire study’s results.

1
Boutzoukas
AE
,
Zimmerman
KO
,
Inkelas
M
, et al
.
School masking policies and secondary SARS-CoV-2 transmission [published online ahead of print March 9, 2022]
.
Pediatrics
.
doi: 10.1542/peds.2022-056687
2
Abaluck
J
,
Kwong
LH
,
Styczynski
A
, et al
.
Impact of community masking on COVID-19: a cluster-randomized trial in Bangladesh
.
Science
.
2022
;
375
(
6577
):
eabi9069
3
Coma
E
,
Catala
M
,
Méndez-Boo
L
, et al
.
Unravelling the role of the mandatory use of face covering masks for the control of SARS-CoV-2 in schools: a quasi-experimental study nested in a population-based cohort in Catalonia, Spain
. .
4
Centers for Disease Control and Prevention
.
Appendices (updated January 4, 2022)
.