Since the onset of the coronavirus disease 2019 (COVID-19) pandemic, several variants of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) have emerged. The most recent B.1.1.529 (Omicron) variant of SARS-CoV-2 was first detected on December 1, 2021, in the United States. Due to its high rate of transmissibility, the Omicron variant soon became the dominant circulating strain and, by January 15, 2022, representing 99.5% of sequenced specimens in the U.S.
Study: Trends in Disease Severity and Health Care Utilization During the Early Omicron Variant Period Compared with Previous SARS-CoV-2 High Transmission Periods — United States, December 2020–January 2022. Image Credit: Dkoi / Shutterstock.com
To understand the impact of Omicron on healthcare utilization and severity of COVID-19, the U.S. Centers for Disease Control and Prevention (CDC) assessed multiple indicators across three high transmission periods. These periods included December 1, 2020, to February 28, 2021 (Winter 2020-2021), July 15 to October 31, 2021, during which the Delta variant was the dominant circulating strain, and December 19, 2021, to January 15, 2022, which was termed Omicron predominance.
In their report published in the Morbidity and Mortality Weekly Report, the researchers compare trends in disease and hospital utilization during the early periods of Omicron circulation to previous SARS-CoV-2 variants in the U.S.
About the study
The current study involved the assessment of data from three surveillance systems related to COVID-19 cases from December 1, 2020, to January 15, 2022. Emergency department (ED) visits, hospital admissions, deaths as well as maximum seven-day moving averages of the daily number of COVID-19 cases during the Omicron period were compared with the Delta and Winter 2020-2021 periods. Moreover, for each period, the hospital admissions, ED visits, and deaths per 1000 cases of COVID-19 were calculated.
Data on the total percentage of hospitalization and staffed inpatient beds used for COVID-19 patients, along with the percentage of patients admitted to intensive care unit (ICU), received invasive mechanical ventilation (IMV), died in the hospital, as well as the length of stay was also collected. Each of these indicators was stratified by age groups of 0 to 17 years, 18 to 50 years, and above 50 years.
The current study reported that the ED visits, hospital admissions, and daily seven-day moving average of COVID-19 cases increased rapidly during the Omicron period. However, during the last week of January 15, 2022, ED visits decreased and were accompanied by the slowing of hospitalization and daily case rates.
The changes in the daily number of cases, ED visits, hospital admissions, and deaths during the Omicron period were 219%, 137%, 31%, and -46%, respectively, as compared to the Winter 2020-2021 period. These changes also differed by 386%, 86%, 76%, and -4%, respectively, as compared to the Delta period.
The largest difference in hospital admission and ED visits was observed in children and adolescents within the 0 to 17 years age group during the Omicron period. The staffed inpatient beds that were in use during the Omicron period were 3.4 and 7.2 percentage points higher as compared to the Winter 2020-2021 and Delta period, respectively. However, ICU bed use was found to be 0.5 percentage points lower and 1.2 percentage points higher as compared to the Winter 2020-2021 and Delta periods, respectively.
Furthermore, the mean length of a hospital stay, along with the percentage of patients who received IMV or died during hospitalization, was lower during the Omicron period as compared to the Winter 2020-2021 and the Delta periods.
Taken together, the current study demonstrates that the SARS-CoV-2 Omicron variant is associated with lower disease severity as compared to the previous SARS-CoV-2 variants. However, the high rate of hospitalization observed during the Omicron period can strain the healthcare system.
Booster doses can be effective in offering protection to individuals during this period where the Omicron variant is the dominant circulating strain. However, in-hospital severity indicators and deaths need to be monitored in order to detect any changes among subpopulations throughout the Omicron period.
The current study had several limitations. First, the data collected did not include all ED visits across the U.S., which may introduce bias. Second, the variation in vaccine coverage was not considered when comparing severity indicators during the assessment of the three periods.
Person-level vaccination data was not available for the current study. Additionally, the inclusion of incidental SARS-CoV-2 infections can affect the severity indicators.
Self-administered tests during the Omicron period may also introduce bias, whereas the co-circulation of both Delta and Omicron may also have an impact on severity indicators. A final limitation is that the current study involves an ecologic analysis of event-based indicators.