During the White House COVID-19 response team meeting on Wednesday, Rochelle Walensky, head of the Centers for Disease Control and Prevention, cited a Kaiser Permanente Southern California study that showed the Omicron variant of COVID-19 has a lower risk of severe illness and death compared with the Delta variant.
- Over the past several weeks, we have seen the number of daily cases increase substantially. The magnitude of this increase is largely related to the omicron variant, which now represents about 98% of the COVID-19 cases in the country. We continue to learn more about omicron with each passing day, including the severity of disease caused by this variant.
Just yesterday, a pre-print study of data from Kaiser Permanente Southern California analyzed by academic partners with CDC collaboration and funding provided key insight into clinical outcomes among patients infected with the omicron variant. This study used mathematical modeling to estimate risk of hospitalization and severe disease from a health care system that provides care to 4.7 million people in Southern California-- 19% of the state's total population-- and noted substantially reduced risk of severe clinical outcomes in patients who are infected with the omicron variant compared with delta.
In the study, there were over 52,000 cases of omicron compared with nearly 17,000 cases of delta. Displayed on this slide are figures from this study. On these graphs, green represents infections with the omicron variant, and purple represents infections with the delta variant. When compared to delta, infections with omicron were associated with a 53% reduction in adjusted risk of symptomatic hospitalization, displayed in the first panel; a 74% reduction in adjusted risk of ICU admission, displayed in the middle panel; and a 91% reduction in adjusted risk of mortality, displayed on the third panel.
No patients with omicron required mechanical ventilation. Additionally, this study found that those infected with omicron who were hospitalized had a shorter duration of hospital stay compared to those with delta. The duration of hospital stays was approximately 70% shorter, with the median of stays being 1.5 days for omicron compared to about 5 days for delta.
Looking at all hospital admissions for omicron, 90% of patients were expected to be discharged from the hospital in three days or less. This study controlled for important key parameters, such as age, sex, prior SARS-CoV-2 infection, prior vaccination, and comorbidities. The data in this study remained consistent with what we are seeing from omicron in other countries, including South Africa and the UK, and provides some understanding of what we can expect over the coming weeks, as cases are predicted to peak in this country.
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. 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. The risk of hospitalization remains low, especially among people who are up to date on their COVID vaccines. However, the staggering rise in cases-- over 1 million new cases each day-- has led to a high number of total hospitalizations.