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New data from Southern California are providing further evidence that the Omicron variant of the coronavirus is causing less severe illness than its Delta cousin, the culprit behind last summer’s wave.

A preliminary study based on medical records from nearly 70,000 Kaiser Permanente Southern California patients “noted substantially reduced risk of severe clinical outcomes in patients who are infected with the Omicron variant compared with Delta,” said Dr. Rochelle Walensky, director of the U.S. Centers for Disease Control and Prevention.

The study — which included more than 52,000 Omicron cases and nearly 17,000 Delta cases within the Kaiser system from Nov. 30 to Jan. 1 — found that, compared with patients infected with Delta, those who had Omicron were 53% less likely to be hospitalized with COVID-19, 74% less likely to be admitted to the intensive care unit, and 91% less likely to die of the disease.

Among patients who were hospitalized, the median length of stay was 1.5 days for patients infected with Omicron and five days for those who had Delta.

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