Background: SARS-CoV-2 transmission frequently occurs within households, yet few studies describe which household contacts and household units are most likely to engage in transmission-interrupting behaviors. Methods: We analyzed a COVID-19 prospective household transmission cohort in North Carolina (April-Oct 2020) to quantify changes in physical distancing behaviors among household contacts over 14 days. We evaluated which household contacts were most likely to ever mask at home and to ever share a bedroom with the index case between Days 7-14. Results: In the presence of a household COVID-19 infection, 24% of household contacts reported ever masking at home during the week before study entry. Masking in the home between Days 7-14 was reported by 26% of household contacts, and was more likely for participants who observed their household index case wearing a mask. Participants of color and participants in high-density households were more likely to mask at home. After adjusting for race/ethnicity, living density was not as clearly associated with masking. Symptomatic household contacts were more likely to share a bedroom with the index case. Working individuals and those with comorbidities avoided sharing a bedroom with the index case. Conclusion: In-home masking during household exposure to COVID-19 was infrequent in 2020. In light of ongoing transmission of SARS-CoV-2, these findings underscore a need for health campaigns to increase the feasibility and social desirability of in-home masking among exposed household members. Joint messaging on social responsibility and prevention of breakthrough infections, reinfections, and long COVID-19 may help motivate transmission-interruption behaviors.

KRM has received grant support Ridgeback Biotherapeutics LP (2020-2021), the Bill & Melinda Gates Foundation, and has HIV collaborations, unrelated to this study, with Gilead Sciences (ongoing). All other authors declare no conflicts of interest related to the content of this manuscript.

Funding for the CO-HOST study and authors was supported by funds and charitable contributions from the UNC Department of Medicine, UNC COVID-19 Response Fund/Health Foundation, a Gillings Innovations Lab Award, and the National Center for Advancing Translational Sciences (NCATS), National Institutes of Health (NIH), through Grant Award Number UL1TR002489. RJR has been funded by the NIH in 2018-2020 (2 T32 GM 8719-21), and from 2022-present (5T32DK007634-33), as well as the UNC Graduate School, GlaxoSmithKline, and CERobs, LLC. WM, CAC, and KRM were supported by the UNC Center for AIDS Research, an NIH funded program (P30 AI050410).

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Ethical approval for the parent study was received from the Institutional Review Board at the University of North Carolina at Chapel Hill (Protocol Number 20-0982), participants gave informed consent before participating, and the parent study conformed to the principles outlined in the Declaration of Helsinki.

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De-identified participant-level data are available upon reasonable request from Rebecca Rubinstein by emailing Rebecca_rubinstein@med.unc.edu. Please cite this manuscript upon use in further publications.