Factors Associated With SARS-CoV-2 Transmission in Settings of High COVID-19 Vaccination Coverage: A Case-Control Study

Despite the availability of effective vaccines, community exposures continue to drive the coronavirus disease 2019 (COVID-19) pandemic across the United States. Though vaccination coverage is high in some regions, uptake has lagged elsewhere (1). Characterization of risk factors remains critically important for informing policies on nonpharmaceutical interventions that target the highest-risk activities and reduce severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) transmission while preserving economic and societal structures. While prior case-control studies have identified diverse risk factors for SARS-CoV-2 transmission (2–4), there is a critical need to understand how increasing vaccination coverage affects the risk of SARS-CoV-2 transmission, particularly with the increased spread of the delta (B.1.617.2) variant (5, 6). We determined risk factors for SARS-CoV-2 transmission in the City and County of San Francisco, California, from April to June 2021, when the proportion of fully vaccinated residents increased from 27.4%...