Division of Epidemiology, School of Public Health, University of California, Berkeley, Berkeley, CA, USA.
Division of Infectious Diseases & Vaccinology, School of Public Health, University of California, Berkeley, Berkeley, CA, USA.
Nat Med. 2022 Sep;28(9):1933-1943. doi: 10.1038/s41591-022-01887-z. Epub 2022 Jun 8.
Epidemiologic surveillance has revealed decoupling of Coronavirus Disease 2019 (COVID-19) hospitalizations and deaths from case counts after emergence of the Omicron (B.1.1.529) severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variant globally. However, assessment of the relative severity of Omicron variant infections presents challenges because of differential acquired immune protection against Omicron and prior variants and because longer-term changes have occurred in testing and healthcare practices. Here we show that Omicron variant infections were associated with substantially reduced risk of progression to severe clinical outcomes relative to time-matched Delta (B.1.617.2) variant infections within a large, integrated healthcare system in Southern California. Adjusted hazard ratios (aHRs) for any hospital admission, symptomatic hospital admission, intensive care unit admission, mechanical ventilation and death comparing individuals with Omicron versus Delta variant infection were 0.59 (95% confidence interval: 0.51-0.69), 0.59 (0.51-0.68), 0.50 (0.29-0.87), 0.36 (0.18-0.72) and 0.21 (0.10-0.44), respectively. This reduced severity could not be explained by differential history of prior infection among individuals with Omicron or Delta variant infection and was starkest among individuals not previously vaccinated against COVID-19 (aHR = 0.40 (0.33-0.49) for any hospital admission and 0.14 (0.07-0.28) for death). Infections with the Omicron BA.2 subvariant were not associated with differential risk of severe outcomes in comparison to BA.1/BA.1.1 subvariant infections. Lower risk of severe clinical outcomes among individuals with Omicron variant infection should inform public health response amid establishment of the Omicron variant as the dominant SARS-CoV-2 lineage globally.
新冠疫情流行病学监测显示，奥密克戎（B.1.1.529）变异株出现后，全球范围内，新冠病毒疾病（COVID-19）住院和死亡人数与病例数已呈现脱钩现象。 然而，由于对奥密克戎变异株和既往变异株获得性免疫保护存在差异，以及检测和医疗实践发生了长期变化，评估奥密克戎变异株感染的相对严重程度存在挑战。在此，我们在南加州一个大型综合医疗系统中发现，与时间匹配的德尔塔（B.1.617.2）变异株感染相比，奥密克戎变异株感染与严重临床结局进展的风险显著降低。调整后的风险比（aHR）显示，奥密克戎变异株感染与德尔塔变异株感染相比，任何住院、有症状住院、入住重症监护病房、机械通气和死亡的风险分别为 0.59（95%置信区间：0.51-0.69）、0.59（0.51-0.68）、0.50（0.29-0.87）、0.36（0.18-0.72）和 0.21（0.10-0.44）。这种严重程度降低不能用奥密克戎或德尔塔变异株感染者既往感染史的差异来解释，在未接种过 COVID-19 疫苗的个体中最为明显（任何住院的 aHR=0.40（0.33-0.49），死亡的 aHR=0.14（0.07-0.28））。与 BA.1/BA.1.1 亚变异株感染相比，奥密克戎 BA.2 亚变异株感染与严重结局风险无差异。在奥密克戎变异株成为全球主导 SARS-CoV-2 谱系的情况下，奥密克戎变异株感染者严重临床结局风险降低应指导公共卫生应对。
