Omicron causes fewer serious illnesses, study suggests

New data from Southern California provides further evidence that the Omicron variant of the coronavirus causes less serious illness than its cousin Delta, the culprit behind last summer’s wave.

A preliminary study, based on medical records of nearly 70,000 patients from Kaiser Permanente in Southern California, “found that the risk of serious clinical consequences is significantly reduced in patients infected with the Omicron variant compared to Delta,” said Dr. Rochelle Walensky, director of the US Center 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 November 30 to January 1 – found that the likelihood of hospitalization compared to patients infected with Delta 53% lower with COVID-19, the chance of admission to the intensive care unit is 74% lower and the chance of dying from the disease is reduced by 91%.

In patients admitted to the hospital, the mean length of stay was 1.5 days for those with Omicron infection and 5 days for those with Delta.


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Another sign of Omicron’s lighter touch: none of the patients who had it required mechanical ventilation.

The results were posted Tuesday on MedRxiv, a website where researchers share preliminary results. The study has not been verified by independent scientists.

“The data in this study is consistent with what we are seeing from Omicron in other countries, including South Africa and the UK, and gives an understanding of what to expect in the coming weeks as cases in that country are likely to peak Walensky said during a briefing on Wednesday.

The new study is the latest, showing that Omicron is milder overall compared to Delta. Nevertheless, the variant is spreading widely and hospitals are seeing an influx of coronavirus-positive patients.

Omicron is the dominant strain of coronavirus in the United States, accounting for an estimated 98% of new cases nationwide, according to the CDC.

Los Angeles County’s hospitals are busy providing medical care as they are hampered by a staff shortage far worse than the coronavirus surge last winter.

Many health care workers burned out by the pandemic have quit, and many who remain have tested positive for the virus and are in isolation at home. And health facilities are busy this year as the demand for non-COVID-19 treatments increases.

In light of the recent surge in cases, Kaiser Permanente Southern California is temporarily postponing all elective surgeries that require hospital stays, it announced on Wednesday.

The hospital system will continue to perform emergency operations, urgent interventions, including those on cancer patients or people whose health would be deteriorated if delayed, and elective outpatient surgeries that do not require an overnight stay in the hospital, the regional director of medical quality said Dr. Nancy Gin.

“We will continue to do everything we can to minimize the impact on our members and the public,” said Gin.

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