New research posted medrxiv* The preprint server shows that the Omicron variant causes less severe COVID-19 symptoms than the earlier severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variant.
There was a 74% lower risk of being admitted to the ICU, a 91% lower risk of death, and none of the patients with Omicron infection required mechanical ventilation. In addition, patients infected with Omicron recovered faster and were discharged sooner than patients with Delta infections.
While omicron may be less severe than other types, the rise in COVID-19 cases is ravaging hospitals and causing severe burns to frontline workers. COVID-19 hospitalization can delay medical care and lead to potentially preventable deaths. The research team recommends practicing several COVID strategies – wearing a mask, isolating when infected, and getting vaccinated – to limit community transmission of omicrons and relieve an overwhelmed health system.
Study: Clinical outcomes in patients infected with SARS-CoV-2 type Omicron (B.1.1.529) in Southern California. Image credit: anushkaniroshan/Shutterstock
Omicron infection rate rising at the end of 2021
Researchers collected and analyzed data on positive COVID-19 cases at Kaiser Permanente Southern California Healthcare System from November 30, 2021 to January 1, 2022.
A total of 88,576 positive COVID-19 cases were reported in outpatients from November 30, 2021 to January 1, 2022. Among hospitalized patients, about 26.6% tested positive.
People with Omicron cases were more likely to have Delta cases than those in their 20s or 30s. Additionally, Delta infections mostly come from low-income neighborhoods, people who identify as white, and have a high risk of comorbidity.
Omicron cases made up 75.5% of COVID-19 cases, including another 51.4% who were tested in inpatient settings.
Trend-wise, the number of COVID-19 cases related to Omicron increased weekly. The only exception was Christmas week, in which the holiday lag lags behind in the processing of tests.
The analyzes showed that recurrent infections were more likely to occur with Omicron than with Delta. People who had a COVID-19 infection 90 or more days after their current infection were 4.45 times more likely to have Omicron cases than Delta cases. In addition, vaccinated people were more likely to be infected with Omicron than Delta.
When the researchers collected samples from 1,477 infected patients for sequencing, 100% of the SARS-CoV-2 isolates found through S gene targeting failure were related to Omicron.
Of the 288,534 people who were outpatients and were later tested and later tested positive, 88 were infected with Omicron and required hospitalization. There were 189 hospitalizations for Delta-related infections.
Characteristics of cases with SGTF and non-SGTF samples were revealed. Panels include (a) trial dates for all cases analyzed (truncated to accommodate ± 1 day of panic on 29 December 2022); (b) the age distribution of all cases analysed; (c) exposure history (pre-documented infection and vaccination) in all cases analyzed; (d) dates of symptomatic hospital admission (29 December 2022 to adjust for palliation of ± 1 day); (e) the age distribution of cases requiring symptomatic hospitalization; and (f) exposure history (pre-documented infection and vaccination) in cases with symptomatic hospitalization. The pink and brown bars correspond to those with and without SGTF, respectively (interpreted as a proxy for SARS-CoV-2 Omicron type infection; Table S1). The totals correspond to samples processed on the RT-PCR TaqPath COVID-19 High-Throughput Combo Kit and do not reflect all cases of KPSC.
Disease Severity in Hospitalized Patients Infected with Omicron vs. Delta
Symptoms occurred in 95.5% of the 88 patients infected with recruited Omicron. Similarly, 98.9% of patients infected with Delta were recruited with symptomatic infection.
About 7 patients infected with the Omicron variant required intensive care, including five who were first identified in outpatient settings. One person died. No one got mechanical ventilation.
Compared with those admitted with infection from the delta variant, 23 were admitted to the ICU, 14 patients died, and 11 patients required ventilation.
The daily risk of requiring mechanical ventilation was significantly higher in patients with delta infection than in patients with Omicron infection.
Approximately 79.7% of Omicron infections reported acute respiratory symptoms prior to hospitalization, compared to 80% reported with delta infections. Once hospitalized, approximately 9.4% of Omicron cases developed respiratory problems. About 16% of Delta infections developed respiratory symptoms upon hospitalization.
Times to severe outcomes in cases with SGTF and non-SGTF infections were first detected in outpatient settings. The panel includes (a) symptomatic hospital admission; (b) ICU admission; (c) initiation of mechanical ventilation; and (d) mortality. Inset plots within each panel show the cumulative probabilities on the same y-axis scale as in panel a. The shaded areas indicate the 95% confidence interval. Green and purple correspond to detection with and without SGTF (interpreted as a proxy for SARS-CoV-2 Omicron type infection), respectively.
Omicron cases showed higher recovery rates after hospitalization than Delta
There were approximately 83.5% of hospitalizations for Omicron cases as of January 1, 2022, compared to 77.8% of hospitalizations for Delta.
All patients hospitalized for Omicron infection were discharged to home or home-based care. Only 92.9% of Delta cases were discharged from the hospital.
People with Omicron infections have about 70% fewer hospital stays than those with Delta infections. The median hospital stay for symptomatic Omicron infection was 1.5 days and 90% of patients were expected to recover within 3 days.
The average hospital stay for Delta infections was about 5 days.
Limitations of the Study
The researchers had a limited amount of time to follow up on all the COVID-19 cases and their hospital discharge rates. Data at discharge was available for 84% of Omicron cases and 78% of Delta cases. Additionally, follow-up data for Omicron infections were scant since they occurred at the end of the study period.
Because there is a potential that COVID-19 testing among Kaiser Permanente Southern California Healthcare Systems differs from testing in the general population, rates of Omicron versus non-Omicron infections and hospitalizations may differ at the population level.
medrxiv Publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be considered conclusive, should guide clinical practice/health-related behavior, or be regarded as established information.