In a recent study published in BMC Public Health, researchers examined the impact of varying COVID-19 vaccination rates on population-level health outcomes across different waves of the virus in the United States. The study focused on the association between time-varying COVID-19 vaccination rates and COVID-19 case-hospitalization risk (CHR), which serves as a proxy for disease severity at an individual level and the burden on healthcare systems at the population level.

Background

By March 1, 2023, COVID-19 had resulted in 1.1 million deaths in the U.S. The effectiveness of COVID-19 vaccines in mitigating the disease and its impact, including the socioeconomic burden and strain on the healthcare system, has been well-documented. However, previous studies assessing vaccine effectiveness were based on individual-level data affected by unquantified factors and inconsistent quality. This led to a lack of high-resolution population-level data in the U.S., hindering the understanding of the real-world associations between available COVID-19 vaccines and COVID-19 CHR over time.

About the Study

The study utilized Generalized Additive Models (GAMs) to explore the relationship between COVID-19 vaccination rates and CHR across 48 U.S. states from April 19, 2021, to March 1, 2022. The model considered dynamic and static factors, including natural immunity from previous SARS-CoV-2 infection, government policies, population engagement levels, local healthcare infrastructure, social vulnerability index (SVI), race/ethnicity, comorbidities, and healthcare expenditures of each state. Additionally, the study examined COVID-19 case incidence rates (CIR) as a separate outcome variable, capturing spatial variations in relative associations. The study period encompassed the pre-Delta, Delta, and Omicron waves of COVID-19, evaluating each independently.

Results

The study revealed several significant findings regarding the effects of COVID-19 vaccines on population-level health outcomes in the U.S. The GAMs demonstrated the relative associations between COVID-19 vaccination rates and CHR, shedding light on the impact of vaccination rates on disease severity and healthcare system burden across different SARS-CoV-2 variant waves.