The results of a statistical study provided some measure as to how much less virulent the Omicron variant is, compared to, so far, the most virulent one, Delta. CDC director Rochelle Walensky called attention to the study, done by researchers at the University of California - Berkeley, in a tweet. The results of 52,297 Omicron cases and 16,982 Delta cases in southern California between November 30, 2021 and January 1, 2022, showed that there was 53% less risk of symptomatic hospitalization with Omicron; 74% less for being put in the ICU; and there were 91% fewer deaths. Further, no Omicron patients required mechanical ventilation.