Real-World Association Between mRNA Vaccination and Infection From the Omicron Strain of SARS-CoV-2: A Population-Level Analysis

INTRODUCTION: Two mRNA vaccines approved in the U.S. have high efficacy against COVID-19 disease from the original strain of SARS-CoV-2. We evaluated the population-level association between vaccination status and COVID-19 infection by age group during the initial wave of the Omicron variant in a diverse population in the Mid-South U.S. METHODS: In this observational population-based cohort study, vaccination information and positive COVID-19 cases in Shelby County, Tennessee, from December 12, 2021 through January 22, 2022 were collected from surveillance data at the Shelby County Health Department (Memphis, Tennessee). Exposure groups included individuals who were unvaccinated, were fully vaccinated, and were fully vaccinated + booster. We calculated incidence rates of COVID-19 diagnosis per person-year among county adult (aged 18+ years) residents in crude form and stratified by age group. RESULTS: In this population-based study, we identified 64.56% fewer COVID-19 infections in the fully vaccinated + booster group and 41.08% fewer in the fully vaccinated group than in the unvaccinated group. CONCLUSIONS: These results confirm and extend the findings of recent immunologic and epidemiologic studies in a racially diverse region of the Mid-South U.S. In stratified analysis, we also found evidence suggesting that vaccine protection against Omicron may increase with age.