Top 5 Takeaways

1. Omicron vs. Delta Severity: Patients hospitalized during the Omicron period had less severe illness compared to those during the Delta period, largely due to higher vaccination rates.
2. Impact of Vaccination: COVID-19 vaccination, especially with a booster dose, was associated with a lower likelihood of ICU admission and death among hospitalized adults.
3. Non-COVID-19 Hospitalizations: Approximately 20% of early Omicron-period hospitalizations were for non–COVID-19 conditions, particularly among younger and vaccinated adults.
4. Demographic Shifts: During the Omicron period, there was an increase in the proportion of fully vaccinated Hispanic adults and a decrease in non-Hispanic White adults among hospitalizations.
5. Therapy Usage: Fewer patients received COVID-19–directed therapies during the Omicron period compared to the Delta period, regardless of vaccination status.

Original Article Author and Citation

Corresponding Author

Peter Chen, peter.chen@cshs.org

Suggested Citation

Modes ME, Directo MP, Melgar M, et al. Clinical Characteristics and Outcomes Among Adults Hospitalized with Laboratory-Confirmed SARS-CoV-2 Infection During Periods of B.1.617.2 (Delta) and B.1.1.529 (Omicron) Variant Predominance — One Hospital, California, July 15–September 23, 2021, and December 21, 2021–January 27, 2022. MMWR Morb Mortal Wkly Rep 2022;71:217–223. DOI: http://dx.doi.org/10.15585/mmwr.mm7106e2

Summary

This study compared the clinical characteristics and outcomes of adults hospitalized with SARS-CoV-2 infection during the periods of Delta and Omicron variant predominance at a single hospital in California. It found that patients hospitalized during the Omicron period had less severe illness, which was largely attributed to higher vaccination rates. COVID-19 vaccination, including booster doses, was associated with a lower likelihood of ICU admission and death. Approximately 20% of early Omicron-period hospitalizations were for non–COVID-19 conditions, especially among younger and vaccinated adults.

Methods

Data were retrospectively abstracted from electronic health records of adults aged ≥18 years with positive RT-PCR SARS-CoV-2 test results admitted to one academic hospital in Los Angeles, California, during July 15–September 23, 2021 (Delta predominant period) and December 21, 2021–January 27, 2022 (Omicron predominant period). Patient demographic and clinical characteristics were compared between the two periods, overall and stratified by vaccination status. Statistical analyses were conducted using R software.

Discussion

The study found that COVID-19 vaccination, particularly with a booster dose, was crucial in reducing the severity of illness during the Omicron period. The increased proportion of fully vaccinated patients during the Omicron period likely contributed to the observed decrease in ICU admissions, IMV, and deaths. Despite the lower severity, the Omicron variant still caused significant lower respiratory illness in hospitalized patients. The findings underscore the importance of continued vaccination efforts to mitigate severe health outcomes associated with SARS-CoV-2 infection.

Conclusion

The study highlights the reduced severity of illness during the Omicron period compared to the Delta period, driven by higher vaccination rates. COVID-19 vaccination, including booster doses, remains critical to minimizing severe health outcomes among adults with SARS-CoV-2 infection. Continued vaccination efforts are essential to manage the healthcare burden and protect public health.

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