Omicron rapidly overtook COVID-19 cases at Houston Methodist, causing 90 percent of all new COVID-19 cases only three weeks after the variant was first identified within the health system. Researchers at Houston Methodist have now released preliminary findings about some of the differences between omicron, delta and alpha patients.
The findings were published Jan. 1 by medRxiv and have yet to be peer reviewed. A comprehensive genome sequencing study in the Houston Methodist system identified 862 symptomatic patients with COVID-19 infections caused by omicron from late November through Dec. 18.
Six things to know:
1. Patients with omicron infections versus alpha or delta were significantly less likely to be hospitalized. Of the 862 total symptomatic patients with sequencing data available, 15.5 of individuals with omicron required hospitalization, compared to 54.5 percent of individuals with alpha and 43 percent of individuals with delta infections.
2. Compared to patients infected with either alpha or delta variants at Houston Methodist, omicron patients had a significantly shorter median hospital length of stay. Omicron patients had a median stay of 2.8 days, compared to 5.4 days for delta patients and 5.1 for patients with alpha infections.
3. Compared to patients with either alpha or delta variants, omicron patients were significantly younger. The median age at hospitalization was 38.9 years for omicron patients, compared to 50 for the alpha variant and 48.2 for delta.
4. Omicron patients required less intense respiratory support, consistent with decreased disease severity.
5. Omicron patients who were fully vaccinated, excluding a third booster dose, had significantly increased vaccine breakthrough rates compared to patients with alpha or delta. Overall, 49.9 percent of all omicron patients (430 of 862) met the CDC definition of vaccine breakthrough cases, compared to 3.2 percent for alpha patients and 24.1 percent for delta.
6. Analysis of individuals with breakthrough cases after receiving a third booster dose of either the Pfizer-BioNTech or Moderna vaccine found that 9.9 percent (85) of the 862 omicron patients met this criteria.