Background: On Dec 14, 2020, the United States initiated a nationwide COVID-19 vaccination campaign. Demonstrating clear population-level impact following vaccine introduction helps to further elucidate and quantify the public-health benefits of vaccination.
Methods: Using a negative binomial regression model we evaluated the ecological association between county-level COVID-19 vaccine uptake and rates of COVID-19 cases and deaths in the United States from April 1, 2021 through October 31, 2021 controlling for a broad set of county-level environmental, sociodemographic, economic, and health-status-related characteristics. County-level data were obtained from several publicly available databases that were merged for analysis.
Findings: After adjustment for county-level characteristics, US counties with ≥ 80% of their residents ≥ 12 years of age fully vaccinated against COVID-19 had 30% (95% CI: 25-35; P < .001) and 46% (38-52; P < .001) lower rates of COVID-19 cases and deaths, respectively, versus those with <50% coverage (reference group). A dose response was observed: counties with 70-79% uptake had 20% (95% CI: 16-24; P < .001) and 35% (29-40; P < .001) lower rates of cases and deaths, respectively; counties with 60-69% uptake had 8% (5-11; P < .001) and 20% (15-24; P < .001) lower rates; and counties with 50-59% uptake had 2% (0-4; P =.09) and 8% (4-12; P < .001) lower rates. Restricting the analysis to the period when the Delta variant was predominant (June 1, 2021 ‒ October 31, 2021) showed similar findings.
Interpretation: Our results showed that US counties with higher proportions of persons ≥ 12 years of age fully vaccinated against COVID-19 had substantially lower rates of COVID-19 cases and deaths-a finding that showed dose response and persisted even in the period when Delta was predominant.
Funding: Pfizer.
Keywords: COVID-19; County; Coverage; Impact; SARS-CoV-2; Transmission; United States; Vaccination.
© 2022 The Authors.