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Assessment of public health interventions to mitigate SARS-CoV-2 transmission and risk factors for infection in California


Vaccination and non-pharmaceutical interventions (NPIs) have been of central importance to mitigate the ongoing COVID-19 pandemic. In collaboration with California Department of Public Health, I designed and managed a test-negative design case-control study to assess risk factors for SARS-CoV-2 infection and the effectiveness of various mitigation strategies including vaccination and the use of face masks. Throughout the study period, a team of trained interviewers placed over 40,000 telephone calls and enrolled over 4,000 total cases and controls, testing positive and negative for SARS-CoV-2, respectively. In Chapter 1, I present COVID-19 vaccine effectiveness estimates using data collected between February ¬– April 2021 when Epsilon (B.1.427 and B.1.429) and Alpha (B.1.1.7) were the dominant SARS-CoV-2 variants of concern circulating in California. I demonstrate mRNA-based vaccines (BNT-162b2 [Pfizer] and mRNA-1273 [Moderna]) conferred substantial protection against documented SARS-CoV-2 infection. However, nearly one-third of participants expressed reluctance to initiate the COVID-19 vaccination series, primarily due to concerns about vaccine side effects or safety. In Chapter 2, I evaluate predictors of SARS-CoV-2 infection amongst a subset of participants who reported history of social contact with a person confirmed or suspected to have been infected with SARS-CoV-2 within 14 days of testing. Among the unvaccinated, participants had a significantly higher odds of testing SARS-CoV-2 positive when social contact was long-lasting (>3 hours), involved a household member, or occurred indoors. Additionally, in the context of these high-risk exposures, I demonstrate mask wearing was most protective among the unvaccinated or partially unvaccinated. Last, in Chapter 3, I estimate the real-world effectiveness of face masks in reducing the risk of acquiring a SARS-CoV-2 infection in public indoors settings. Participants self-reported their frequency of mask use and the type of mask typically worn in public indoor settings. I found that any mask use in public indoor settings reduced the odds the wearer acquired a SARS-CoV-2 infection and mask use exhibited additional protection with increasing frequency of use. Upgrading face masks to masks with higher filtration capacity (N95/KN95s) conferred additional protection. This work has demonstrated the value of case-control studies to rapidly collect real-time data to address and monitor emerging issues in the COVID-19 pandemic and advance public health policy.

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