Outcomes Among Adults With SARS-CoV-2 Infection Delta/Omicron

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

Matthew E Modes, MD; Michael P. Directo, MD; Michael Melgar, MD; Lily R. Johnson, MPH; Haoshu Yang, PharmD; Priya Chaudhary, MBBS; Susan Bartolini; Norling Kho; Paul W. Noble, MD; Sharon Isonaka, MD; Peter Chen, MD

Disclosures

Morbidity and Mortality Weekly Report. 2022;71(6):217-223. 

In This Article

Abstract and Introduction

Introduction

In mid-December 2021, the B.1.1.529 (Omicron) variant of SARS-CoV-2, the virus that causes COVID-19, surpassed the B.1.617.2 (Delta) variant as the predominant strain in California.§ Initial reports suggest that the Omicron variant is more transmissible and resistant to vaccine neutralization but causes less severe illness compared with previous variants.[1–3] To describe characteristics of patients hospitalized with SARS-CoV-2 infection during periods of Delta and Omicron predominance, clinical characteristics and outcomes were retrospectively abstracted from the electronic health records (EHRs) of adults aged ≥18 years with positive reverse transcription–polymerase chain reaction (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, 339 patients) and December 21, 2021–January 27, 2022 (Omicron predominant period, 737 patients). Compared with patients during the period of Delta predominance, a higher proportion of adults admitted during Omicron predominance had received the final dose in a primary COVID-19 vaccination series (were fully vaccinated) (39.6% versus 25.1%), and fewer received COVID-19–directed therapies. Although fewer required intensive care unit (ICU) admission and invasive mechanical ventilation (IMV), and fewer died while hospitalized during Omicron predominance, there were no significant differences in ICU admission or IMV when stratified by vaccination status. Fewer fully vaccinated Omicron-period patients died while hospitalized (3.4%), compared with Delta-period patients (10.6%). Among Omicron-period patients, vaccination was associated with lower likelihood of ICU admission, and among adults aged ≥65 years, lower likelihood of death while hospitalized. Likelihood of ICU admission and death were lowest among adults who had received a booster dose. Among the first 131 Omicron-period hospitalizations, 19.8% of patients were clinically assessed as admitted for non–COVID-19 conditions. Compared with adults considered likely to have been admitted because of COVID-19, these patients were younger (median age = 38 versus 67 years) and more likely to have received at least one dose of a COVID-19 vaccine (84.6% versus 61.0%). Although 20% of SARS-CoV-2–associated hospitalizations during the period of Omicron predominance might be driven by non–COVID-19 conditions, large numbers of hospitalizations place a strain on health systems. Vaccination, including a booster dose for those who are fully vaccinated, remains critical to minimizing risk for severe health outcomes among adults with SARS-CoV-2 infection.

Periods of Delta and Omicron predominance (July 15–September 23, 2021, and December 21, 2021–January 27, 2022, respectively) were defined to correspond to peaks in SARS-CoV-2 hospitalizations during which each variant accounted for ≥50% of sequenced SARS-CoV-2 isolates in California (Supplementary Figure, https://stacks. cdc

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*These authors contributed equally to this report.
These senior authors contributed equally to this report.
§ https://covid19.ca.gov/variants/
This flagging can be triggered in one of two ways: either by a laboratory report indicating a positive SARS–CoV-2 RT-PCR test result from any time during hospitalization or during a 14-day lookback window preceding admission, which included tests performed in ambulatory and inpatient settings, or by admitting physician confirmation of RT-PCR positivity from an outside facility via patient interview, during which time a patient was queried about positive RT-PCR test results and any related COVID-19 symptoms over the preceding 14 days. Hospitalizations were included in the study if they occurred among adults without another hospitalization associated with a positive SARS-CoV-2 RT-PCR result during the preceding 90 days, or if there was a hospitalization associated with a positive RT-PCR result during the preceding 90 days, but the patient's symptoms had resolved before readmission as determined by the admitting provider.
**Fully vaccinated adults were those who were not immunocompromised and had received the second of a 2-dose COVID-19 vaccine series or a single dose of a 1-dose product ≥14 days before receiving a positive SARS-CoV-2 test result associated with their hospitalization. Immunocompromised adults were considered fully vaccinated if they had received a third dose of a 3-dose primary series or a single dose of a 1-dose product ≥14 days before receiving a positive SARS-CoV-2 test result associated with their hospitalization. Fully vaccinated adults were considered to have received a booster dose if they had received an additional dose (third or fourth) of an mRNA COVID-19 vaccine ≥14 days before receiving a positive SARS-CoV-2 test result associated with their hospitalization. Adults whose positive SARS-CoV-2 test date was ≥14 days after the first dose of a 2-dose series (or second dose of a 3-dose series) but <14 days after receipt of the second dose (or third dose) were considered partially vaccinated, as were those who had received only a single dose of a 2-dose series (or 1 or 2 doses of a 3-dose series). Adults with no documented receipt of any COVID-19 vaccine dose before the test date were considered unvaccinated.
††Chart review included notes by the emergency department provider, admitting provider, initial infectious disease consultant (when consulted), and discharging provider when available. Admissions associated with a positive SARS-CoV-2 RT-PCR result were classified as likely due to COVID-19 if the admitting provider affirmed that COVID-19 was the reason for admission or, in the absence of explicit determination, if reviewers could not determine a clear alternative reason for admission that was not plausibly linked to SARS-CoV-2 infection. Alternative reasons for admission included uncomplicated labor, a surgical procedure, trauma, psychiatric care, or a medical diagnosis not plausibly linked to COVID-19 (cellulitis [six patients], gastrointestinal bleeding [two], small bowel obstruction [two], and osteomyelitis [one]). Exacerbations of chronic conditions (e.g., congestive heart failure, chronic obstructive pulmonary disease, and asthma) were attributed to COVID-19. Any positive RT-PCR test results ≥7 days after initial negative test results on admission were considered to represent nosocomial SARS-CoV-2 infections, and therefore, the admission was not attributed to COVID-19. This applied to three hospitalizations included in this report.
§§ https://www.cdc.gov/media/releases/2021/p0924-booster-recommendations-.html
¶¶45 C.F.R. part 46; 21 C.F.R. part 56.

Recommendations

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