Factors associated with onward SARS-CoV-2 transmission among household and dormitory contacts of cases in Brunei Darussalam, August 2021 – February 2022: A retrospective cohort study

• We reported COVID-19 transmission during Delta and Omicron variant waves in Brunei. • Analysis was done for close contacts in household and worker dormitory cluster types. • SI was shorter in household than dormitory, but their SAR were similar. • Higher aORs were found among older and immediate family members in households. • Highlight more studies on the role of housing composition in transmission dynamics. We determine the factors associated with contacts testing positive within a typical household and worker dormitory clusters during the COVID-19 Delta and Omicron waves. Retrospective analyses of national COVID-19 cases and contacts datasets in Brunei Darussalam, from August 2021 to mid-February 2022. We identified 22,540 laboratory-confirmed cases, whereby 50.9% and 25.9% were from household and dormitory clusters, respectively. The median (IQR) SI for household [3 days (2 – 5)] was shorter than that of dormitory [5 days (3 - 9), p-value < 0.001]. Merging with the contact dataset provided 14,289 household (and 10,900 dormitory) contacts from 2,817 (and 1,071) index cases. The overall SAR was similar for household (31.7% [95% Confidence Interval (95%CI): 31.0, 32.5]) and dormitory contacts (27.4% [95%CI: 26.6, 28.3]). For all contacts, adjusted odds ratios (aORs) increase with decreasing vaccine doses acquired at exposure, and if their index cases were symptomatic and infected during the Omicron period. aORs were higher among older household contacts (>40 years) and immediate family members of their index cases. In contrast, aORs for dormitory contacts were higher among male index cases. Our findings suggest a significant role of housing composition in within-household transmission dynamics.