Comparative hospitalization and mortality risk in a US population during the Omicron and Delta periods

In a recent report published in the US Centers for Disease Control and Prevention (US-CDC) Weekly morbidity and mortality report (MMWR)Researchers compared hospital mortality across periods of the coronavirus disease 2019 (COVID-19) pandemic.

Study: Mortality risk among hospitalized patients primarily due to COVID-19 during the Omicron and Variable Delta pandemic periods - United States, April 2020 - June 2022. Image Credit: Thaiview/Shutterstock
Stady: Mortality risk among patients hospitalized primarily with COVID-19 during the Omicron and Delta pandemic periods – United States, April 2020 – June 2022. Image Credit: Thaiview / Shutterstock


Studies have demonstrated that the risk of severe COVID-19 infection and in-hospital mortality increases with age, disability, and pre-existing health conditions (comorbidities). The worrisome variant of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) (VOC) Omicron is more contagious but causes much less severe disease. Additionally, by the time Omicron appeared, the majority of the world’s population had developed high levels of vaccine- or infection-induced immunity.

Consequently, the proportion of the US population with infection-induced antibodies to SARS-CoV-2 increased from 33% in December 2021 to 57% by February 2022. During the same time, the medical community has made many advances in oral COVID-19 treatments. For patients at risk of severe disease. Together, this led to a marked decrease in other measures of COVID-19 severity during the period of Omicron’s dominance. For example, there was a decrease in the number of admissions to the intensive care unit (ICU) and mandatory intermittent ventilation (IMV).

about studying

In this study, researchers retrieved data on hospitalizations and deaths related to COVID-19 from 678 hospitals in the United States registered in the Premier Healthcare’s COVID-19 Release Database (PHD-SR). An expired discharge case indicated an in-hospital death linked to COVID-19. The researchers used the . file International Classification of Diseases, 10th revision, clinical modification (ICD-10-CM) Code U07.1 to identify hospitalizations related to COVID-19.

The team performed analyzes for each patient by selecting each patient’s last COVID-19 hospitalization record during the Delta (July to October 2021), the early Omicron (January to March 2022), and the later Omicron (April to June 2022) periods.

They described sociodemographic planning, disease severity, and hospital characteristics to calculate the crude mortality risk (cMR), that is, deaths per 100 hospital admissions, for each predefined study period. cMR calculations included total deaths and deaths related to COVID-19 and deaths not related to COVID-19.

The study model estimated adjusted mortality risk differences (aMRDs) and adjusted mortality risk ratios (aMRRs), which determine the absolute risk and relative risks of in-hospital death, respectively. Furthermore, the researchers conducted meta-analyses for three pre-delta periods between April 2020 and June 2021.

they used z . tests To compare cMR, aMRDs and aMRR across the COVID-19 pandemic periods, where p < 0.05 indicates statistical significance. Finally, researchers provided aMRDs and aMRRs for in-hospital mortality during the early Omicron versus delta and later Omicron versus delta periods using multivariate generalized estimation equation (GEE) models.


According to the PHD-SR records, 1,072,106 hospital admissions related to COVID-19 and 128,517 in-hospital deaths occurred between April 2020 and June 2022. The cMR rate among hospitalized patients primarily for COVID-19 was 15.1 and 13.1 and 4.9 during the delta, early Omicron, and later Omicron periods, with the cMR range from 9.9 to 16.1 during the three pre-delta periods.

With respect to the pattern of cMRs, cMR was 1 to 2 percentage points higher for COVID-19 hospital admissions than for total COVID-19 hospitalizations through December 2021. As COVID-19-related hospitalizations started declining during the early Omicron period, increased cMR difference up to 3.5 percentage points back to 1 to 2 percentage points back in the later Omicron period.

Compared to the delta period, the in-hospital mortality rate among patients hospitalized primarily with COVID-19 was 0.69 and 0.24 times during the early and later Omicron periods, respectively. Notably, cMR decreased from 15.1% to 4.9% between the delta and subsequent omicron periods, despite the majority of hospital admissions for high-risk patients.

The risk of death did not differ between the Omicron and Delta periods for patients younger than 18 years of age. During the subsequent Omicron period, 81.9% of in-hospital deaths occurred among adults over 65 years of age. Similarly, 73.4% of individuals with three or more comorbidities died in hospitals during this time. However, the study results could not confirm whether these patients with comorbidities had experienced respiratory complications associated with COVID-19 or other acute or chronic conditions exacerbated by SARS-CoV-2 infection.


During Omicron’s predominance period, the rate of cMR in hospitalizations associated with COVID-19 decreased to 4.9%. This cMR was approximately one third of the observed cMR in the delta-control period and less than any other period of the COVID-19 pandemic. Similarly, in-hospital mortality decreased for all patient groups during the subsequent Omicron period. Furthermore, most hospitalizations and deaths occurred among patients over 65 years of age, patients with disabilities, and those with three or more comorbidities.

In general, in the late-dominance period of Omicron, patients with COVID-19 at lower risk were not hospitalized more often, but those without severe outcomes and significantly lower risk. Thus, the study findings highlighted the need for ongoing vaccination, early treatment, and non-pharmacological interventions to prevent COVID-19-related deaths, especially in high-risk individuals.

Importantly, there is a need to continue monitoring COVID-19-related hospitalizations and deaths amid the development of protective immunity, whether induced by infection or vaccine, and the emergence of novel SARS-CoV-2 volatile compounds to inform public health strategies.

*Important note

medRxiv publishes preliminary scientific reports that have not been peer-reviewed and therefore should not be considered conclusive, guide clinical practice/health-related behavior, or be treated as established information.

Source link

Related Posts