Study estimates omicron patients at ‘substantially reduced risk’ than delta patients

Nursing coordinator Beth Springer looks into a patient's room in a COVID-19 ward at the Willis-Knighton Medical Center in Shreveport, La. on Tuesday, August 17, 2021.
Associated Press/Gerald Herbert

A preprint study released Tuesday estimated that patients infected with the omicron variant were at “substantially reduced risk” of severe outcomes than delta patients, aligning with earlier research suggesting omicron cases may cause less severe disease.

The study, which has yet to be peer-reviewed, used modeling to determine that the omicron strain was about half as likely to send patients to California hospitals than the delta variant. Patients hospitalized with the omicron strain were also more likely to have shorter hospital stays than delta patients. 

Centers for Disease Control and Prevention (CDC) Director Rochelle Walensky called the study’s results “consistent” with other research during a White House briefing Wednesday.

“The data in this study remain consistent with what we are seeing from omicron in other countries, including South Africa and the U.K., and provide some understanding of what we can expect over the coming weeks, as cases are predicted to peak in this country,” she said. 

Still, Walensky warned that the high transmissibility of omicron has caused an exponential increase in COVID-19 cases, which regardless of its severity is putting pressure on hospitals. 

“While we are seeing early evidence that omicron is less severe than delta and that those infected are less likely to require hospitalization, it’s important to note that omicron continues to be much more transmissible than delta,” she said. 

“The sudden and steep rise in cases due to omicron is resulting in unprecedented daily case counts, sickness, absenteeism and strains on our health care system,” she continued. 

The study involved more than 52,000 omicron patients and almost 17,000 delta patients within the Kaiser Permanente Southern California health care system between Nov. 30 and Jan. 1, when both variants were spreading. 

Researchers found a 53 percent reduced risk for hospitalization and a 74 percent reduced risk for intensive care unit admission among omicron patients. No omicron patients needed to go on a ventilator, compared to 11 delta patients. One person infected with omicron died, while the system recorded 14 fatalities among patients with delta.  

The median length of hospital stay among omicron patients was also almost 3.5 days shorter than those infected with delta.  

As the more transmissible strain, the omicron variant became dominant during the study’s period. Now, the CDC estimates that 98 percent of all COVID-19 cases in the country are caused by omicron, Walensky said on Wednesday.

Cases have spiked nationwide since mid-December, reaching an average of more than 750,000 new daily cases that dwarfs earlier surges. Hospitalizations and deaths are also climbing to almost 20,000 and 1,600 per day, respectively, Walensky said.

The CDC director called on Americans to help strained hospitals and health care systems by masking in public indoor settings and getting vaccinated and boosted, noting the lower risk of hospitalization among those “up to date” with their COVID-19 shots.

“We must do — all of us do our part to protect our hospitals and our neighbors and reduce the further spread of this virus,” she said at the briefing.

Tags COVID-19 Delta Delta variant hospitalizations hospitals omicron Omicron variant Pandemic Rochelle Walensky variants
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