This study, from EHR and databases for 5 Johns Hopkins hospitals between 9/2020 and 5/2022, assesses approximately 4,500 patients hospitalized for COVID-19 grouped by SARS-CoV-2 variant, and previous infection or vaccination. The primary outcome was severe disease (treatment with high flow nasal cannula, non-invasive PPV, or IMV), or death. The variant was determined by whole genome sequencing (22%), or admission when > 95% of cases were a single variant. The probability of severe disease for patients without prior vaccination or infection was 0.28 for ancestral, 0.35 for alpha, 0.36 for delta and 0.28 for omicron and the relative risk of severe disease, compared to ancestral, was 1.3 for delta and 0.94 for omicron. When compared to those without prior infection or vaccination, the hazard ratio of severe disease was 0.4 for patients with prior infection or vaccination. There was no difference in the incidence of severe disease between the delta and omicron variants in this group.

https://academic.oup.com/cid/advance-article/doi/10.1093/cid/ciac957/6931752