Early evidence of COVID-19 vaccine effectiveness within the general population of California (preprint)

ABSTRACT

Importance Evidence is needed to determine COVID-19 vaccine effectiveness under real world conditions of use. Objective: To determine the effectiveness of authorized vaccines against COVID-19 in the context of substantial circulation of SARS-CoV-2 variants of concern, and identify vaccine uptake barriers. Design: We recruited cases (testing positive) and controls (testing negative) based on SARS-CoV-2 molecular diagnostic test results from 24 February-7 April 2021. Controls were individually matched to cases by age, sex, and geographic region. We identified cases and controls via random sampling within predetermined demographic strata. We conducted enrollment and administered study questionnaires via telephone-based facilitated interviews. Setting: Population-based surveillance of all SARS-CoV-2 molecular diagnostic testing reported to the California Department of Public Health. During the study period, 69% of sequenced SARS-CoV-2 isolates in California belonged to variants of concern B.1.1.7, B.1.427, or B.1.429. Participants: We enrolled 645 adults aged [≥]18y, including 325 cases and 320 controls Exposures We assessed participants' self-reported history of COVID-19 vaccine receipt (BNT162b2 and mRNA-1273). Individuals were considered fully vaccinated two weeks after second dose receipt. Main Outcomes and Measures: The primary endpoint was a positive SARS-CoV-2 molecular test result. For unvaccinated participants, we assessed willingness to receive vaccination, when eligible. We measured vaccine effectiveness via the matched odds ratio of prior vaccination, comparing cases with controls. Results: Among 325 cases, 23 (7%) and 13 (4%) received BNT162b2 and mRNA-1273, respectively; 8 (2%) were fully vaccinated with either product. Among 260 controls, 49 (19%) and 49 (19%) received BNT162b2 and mRNA-1273, respectively; 42 (16%) were fully vaccinated with either product. Among fully vaccinated individuals, vaccine effectiveness was 86% (95% confidence interval 67-94%). Vaccine effectiveness was 66% (-69% to 93%) and 78% (23% to 94%) one week following a first and second dose, respectively. Among unvaccinated participants, 39% of those residing in rural regions and 23% of those residing in urban regions reported hesitancy to receive COVID-19 vaccines, when eligible. In contrast, vaccine hesitancy did not significantly differ by age, sex, household income, or race/ethnicity. Conclusions and Relevance Ongoing vaccination efforts are preventing SARS-CoV-2 infection in the general population in California. Vaccine hesitancy presents a barrier to reaching coverage levels needed for herd immunity.