ABSTRACT
INTRODUCTION: Initial reports suggest the B.1.1.529 (Omicron) variant of SARS-CoV-2 causes less severe disease compared with the B.1.617.2 (Delta) variant, though more widespread vaccination contributed to these findings. Little is known about clinical characteristics and outcomes of patients with SARS-CoV-2 infection requiring intensive care during periods of Delta and Omicron variant predominance. AIM: To examine and compare characteristics of critically ill adults with SARS-CoV-2 infection during periods of Delta and Omicron variant predominance. METHODS: We conducted a retrospective cohort study of critically ill adults with SARS-CoV-2 infection at one academic hospital in Los Angeles during Delta (15 July 2021-23 September 2021) and Omicron (21 December 2021-27 January 2022) predominance. Patient characteristics were compared between Delta-period and Omicron-period hospitalisations, overall and stratified by vaccination status. RESULTS: 79 adults required intensive care during the Delta predominance period and 116 during the Omicron predominance period. We found similar proportions of intensive care unit admissions occurring in fully vaccinated patients between the two periods, despite Los Angeles County data revealing an almost 60% increase in the proportion of SARS-CoV-2 hospitalisations occurring in fully vaccinated persons. There was no difference in the need for invasive mechanical ventilation (IMV). Among those who required IMV, the median duration of IMV was shorter overall (Delta=18 days; Omicron=8 days; p=0.006) and among unvaccinated persons (Delta=19 days; Omicron=8.5 days; p=0.018). Among unvaccinated persons, the median intensive care unit length of stay was shorter (Delta=12 days; Omicron=5 days; p=0.037) during Omicron predominance. There was no difference in the proportion of patients who died while hospitalised. CONCLUSIONS: In this single-hospital study, critically ill patients with SARS-CoV-2 infection experienced less severe respiratory disease during Omicron predominance, likely due to reduced variant-specific virulence. Vaccination likely reduced development of critical illness in adults with SARS-CoV-2 infection during Omicron predominance.
Subject(s)
COVID-19 , Humans , Adult , COVID-19/epidemiology , COVID-19/therapy , SARS-CoV-2 , Critical Illness/epidemiology , Critical Illness/therapy , Retrospective Studies , HospitalsABSTRACT
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.