A new study from Kaiser Permanente Southern California found that omicron infections were tied to significantly lower risks of hospitalization, ICU admission, and death than delta infections—but experts warn against dismissing the risks from omicron as "mild."

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Omicron tied to lower hospitalization, death rates, preprint study suggests

For the study—which has not yet been peer reviewed, and which was conducted through funding and collaboration with CDC—researchers analyzed clinical and epidemiological data from individuals who tested positive for Covid-19 within the Kaiser Permanente Southern California health care system between Nov. 30, 2021, and Jan. 1, 2022.

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Researchers analyzed data from 52,297 omicron cases and 16,982 delta cases. They estimated that, compared to infections with the delta variant, omicron infections were associated with a 53% reduction in symptomatic hospitalizations, a 74% reduction in ICU admissions, and a 91% reduction in deaths.

However, the statistical power of the study was relatively limited. For instance, while the researchers' best estimate was that omicron was associated with a 91% lower risk of death than delta, the confidence interval for that estimate ranged from just a 25% reduction all the way up to a 99% reduction.

The study also found that omicron patients had shorter hospital stays than delta patients. "The duration of hospital stays was approximately 70% shorter, with the median of stays being 1.5 days for omicron, compared to about five days for delta," said CDC director Rochelle Walensky.

In fact, among the study's hospitalized omicron patients, "90% of patients were expected to be discharged from the hospital in three days or less," she added.

Omicron infections may be milder, but omicron isn't 'mild,' experts say

Since early evidence appears to suggest—so far—that omicron may not be as severe as other variants, some have labeled omicron as "mild," The Atlantic reports. But experts caution against that characterization.

One reason is that, even though omicron's symptoms may be mild for many people—especially those who are vaccinated and boosted—the variant remains extremely dangerous to others, especially those who are unvaccinated or have preexisting conditions.

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Lekshmi Santhosh, a critical-care physician at University of California, San Francisco, has seen omicron worsen chronic health issues to the point where they turn fatal. "You could say they didn't die of Covid," she said. "But if they didn't have Covid, they wouldn't have had this issue."

Separately, Akiko Iwasaki, an immunologist at Yale University, warned that the dismissal of omicron's risks represents "a very dangerous attitude." Iwasaki voiced concern over a potential wave of people suffering from long Covid, which can appear even after an individual has an infection that is initially symptom-free. "Some of these people are bedridden, unable to return to work for months," she said. "There is nothing mild about it."

Another issue is that, even though a relatively small fraction of omicron patients require hospitalization, the variant has spread so quickly that it's overwhelming hospitals and straining society more broadly. Walensky noted that omicron has resulted in "unprecedented daily case counts, sickness, absenteeism, and strains on our health care system."

And because so many millions of people have been infected during the omicron surge, the total number of Covid-related deaths remains staggering. As the Washington Post reports, the United States continues to experience the equivalent of one 9/11 death toll every two days. (Lewnard et al., medRxiv, 1/11; Gonzalez, Axios, 1/12; Wu, The Atlantic, 1/12; Washington Post, 1/12)