On Jan. 11, 2022, researchers from the University of California, Berkeley examined the virulence of the omicron variant of SARS-CoV-2 in comparison with the delta variant (Lewnard JA, Hong VX, Patel MM, et al. Clinical outcomes among patients infected with omicron (B.1.1.529) SARS-CoV-2 variant in Southern California [Preprint]. Medrxiv. 2022 January 11).

Researchers compared 52,297 cases of COVID-19 caused by the omicron variant with 16,982 cases caused by the delta variant. Rates of hospitalization, intensive care unit admissions, requirement for mechanical ventilation, and mortality were substantially higher for infections caused by the delta variant than those caused by the omicron variant. The authors concluded, “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 stays.”

Although several reports from the media have suggested that infection with omicron, since it appears to be less virulent, would be an effective way to provide long-term protection against serious illness caused by SARS-CoV-2 in the future, it should be noted that there is a difference between the terms “less virulent” and “avirulent.” The omicron variant can still cause hospitalization and death from COVID-19.

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