Summary of data sources.

Background Given the waning of vaccine effectiveness and the shifting of the most dominant strains in the U.S., it is imperative to understand the association between vaccination coverage and Severe Acute Respiratory Syndrome coronavirus 2 (SARS-CoV-2) disease and mortality at the community levels and whether that association might vary according to the dominant SARS-CoV-2 strains in the U.S. Methods Generalized estimating equations were used to estimate associations between U.S. county-level cumulative vaccination rates and booster distribution and the daily change in county-wide Coronavirus 2019 disease (COVID-19) risks and mortality during Alpha, Delta and Omicron predominance. Models were adjusted for potential confounders at both county and state level. A 2-week lag and a 4-week lag were introduced to assess vaccination rate impact on incidence and mortality, respectively. Results Among 3,073 counties in 48 states, the average county population complete vaccination rate of all age groups was 50.79% as of March 11th, 2022. Each percentage increase in vaccination rates was associated with reduction of 4% (relative risk (RR) 0.9607 (95% confidence interval (CI): 0.9553, 0.9661)) and 3% (RR 0.9694 (95% CI: 0.9653, 0.9736)) in county-wide COVID-19 cases and mortality, respectively, when Alpha was the dominant variant. The associations between county-level vaccine rates and COVID-19 incidence diminished during the Delta and Omicron predominance. However, each percent increase in people receiving a booster shot was associated with reduction of 6% (RR 0.9356 (95% CI: 0.9235, 0.9479)) and 4% (RR 0.9595 (95% CI: 0.9431, 0.9761)) in COVID-19 incidence and mortality in the community, respectively, during the Omicron predominance. Conclusions Associations between complete vaccination rates and COVID-19 incidence and mortality appeared to vary with shifts in the dominant variant, perhaps due to variations in vaccine efficacy by variant or to waning vaccine immunity over time. Vaccine boosters were associated with notable protection against Omicron disease and mortality.研究背景 鉴于美国疫苗保护效力逐渐衰减，且主流新冠毒株不断更迭，明确社区层面疫苗接种覆盖率与严重急性呼吸综合征冠状病毒2（SARS-CoV-2）感染发病及死亡之间的关联，以及该关联是否会随美国境内主流SARS-CoV-2毒株的变化而改变，具有重要的现实意义。 研究方法 采用广义估计方程（Generalized estimating equations），评估美国县级层面累计疫苗接种率、加强针接种分布，与Alpha、Delta及Omicron毒株主导流行期间全县范围内新型冠状病毒肺炎（COVID-19）感染风险及死亡人数的日变化之间的关联。模型针对县级及州级层面的潜在混杂因素进行了校正。分别设置2周及4周的滞后周期，以分别评估疫苗接种率对发病与死亡的影响。 研究结果 本次研究纳入美国48个州的3073个县级行政区，截至2022年3月11日，所有年龄段人群的县级平均全程疫苗接种率为50.79%。当Alpha为优势流行毒株时，县级疫苗接种率每提升1个百分点，全县范围内的COVID-19确诊病例数与死亡人数分别减少4%（相对危险度（relative risk, RR）=0.9607，95%置信区间（confidence interval, CI）：0.9553~0.9661）与3%（RR=0.9694，95%CI：0.9653~0.9736）。在Delta及Omicron毒株主导流行期间，县级疫苗接种率与COVID-19发病之间的关联有所减弱。但在Omicron毒株流行期间，加强针接种率每提升1个百分点，社区内的COVID-19发病与死亡人数分别减少6%（RR=0.9356，95%CI：0.9235~0.9479）与4%（RR=0.9595，95%CI：0.9431~0.9761）。 研究结论 全程疫苗接种率与COVID-19发病及死亡之间的关联，似乎随优势流行毒株的更迭而发生变化，这可能源于不同毒株对应的疫苗保护效力差异，或是疫苗免疫力随时间推移逐渐衰减。加强针接种对Omicron感染所致的发病与死亡均具有显著的保护作用。