Berkeley, CA—Data from a large California healthcare system supports evidence that SARS-CoV-2 infections with presumed Omicron variant infection were associated with substantially reduced risk of severe clinical outcomes and shorter durations of hospital stay compared with the Delta variant.

The preprint article appearing on the medRxiv preprint server website points out that the Omicron (B.1.1.529) variant of SARS-CoV-2 has spread rapidly and now accounts for most infections in the United States as of December 2021.

University of California Berkely–led researchers said they conducted the study because risk of severe outcomes associated with Omicron infections, as compared to earlier SARS-CoV-2 variants remained unclear.

To remedy that, the study team analyzed clinical and epidemiologic data from cases testing positive for SARS-CoV-2 infection within the Kaiser Permanente Southern California healthcare system from November 30, 2021, to January 1, 2022. The S gene target failure (SGTF) as assessed by the ThermoFisher TaqPath ComboKit assay was used as a proxy for Omicron infection.

The focus was on time to any hospital admission and hospital admissions associated with new-onset respiratory symptoms, ICU admission, mechanical ventilation, and mortality among cases with Omicron and Delta (non-SGTF) variant infections.

The analysis included 52,297 cases with SGTF (Omicron) and 16,982 cases with non-SGTF (Delta [B.1.617.2]) infections. Researchers found that hospital admissions occurred among 235 (0.5%) and 222 (1.3%) of cases with Omicron and Delta variant infections.

"Among cases first tested in outpatient settings, the adjusted hazard ratios for any subsequent hospital admission and symptomatic hospital admission associated with Omicron variant infection were 0.48 (0.36-0.64) and 0.47 (0.35-0.62), respectively," the study notes. "Rates of ICU admission and mortality after an outpatient positive test were 0.26 (0.10-0.73) and 0.09 (0.01-0.75) fold as high among cases with Omicron variant infection as compared to cases with Delta variant infection."

In fact, the authors point out that no cases with Omicron variant infection received mechanical ventilation, compared with 11 cases with Delta variant infections throughout the period of follow-up (two-sided P <.001).

In addition, median duration of hospital stay was 3.4 (2.8-4.1) days shorter for hospitalized cases with Omicron variant infections compared with hospitalized patients with Delta variant infections. The authors say that represented a 69.6% (64.0%-74.5%) reduction in hospital length of stay. "During a period with mixed Delta and Omicron variant circulation, SARS-CoV-2 infections with presumed Omicron variant infection were associated with substantially reduced risk of severe clinical endpoints and shorter durations of hospital stay," researchers conclude.

The study funded by the CDC was discussed at a White House briefing by CDC Director Rochelle Walensky, MD, MPH, who pointed out that deaths were down about 91% from Omicron to Delta.

She emphasized that the results of the study were consistent with what has been seen in other areas and other countries. Dr. Walensky cautioned, however, that the Omicron variant is significantly more transmissible than the Delta variant and can still overwhelm the healthcare system and affect the nation's business, even if it is less severe.

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