Comparison of outcomes from COVID infection in pediatric and adult patients before and after the emergence of Omicron

Abstract

Background The Omicron SARS-CoV-2 variant is rapidly spreading in the US since December 2021 and is more contagious than earlier variants. Currently, data on the severity of the disease caused by the Omicron variant compared with the Delta variant is limited. Here we compared 3-day risks of emergency department (ED) visit, hospitalization, intensive care unit (ICU) admission, and mechanical ventilation in patients who were first infected during a time period when the Omicron variant was emerging to those in patients who were first infected when the Delta variant was predominant. Method This is a retrospective cohort study of electronic health record (EHR) data of 577,938 first-time SARS-CoV-2 infected patients from a multicenter, nationwide database in the US during 9/1/2021-12/24/2021, including 14,054 who had their first infection during the 12/15/2021-12/24/2021 period when the Omicron variant emerged (Emergent Omicron cohort) and 563,884 who had their first infection during the 9/1/2021-12/15/2021 period when the Delta variant was predominant (Delta cohort). After propensity-score matching the cohorts, the 3-day risks of four outcomes (ED visit, hospitalization, ICU admission, and mechanical ventilation) were compared. Risk ratios, and 95% confidence intervals (CI) were calculated. Results Of 14,054 patients in the Emergent Omicron cohort (average age, 36.4), 27.7% were pediatric patients (<18 years old), 55.4% female, 1.8% Asian, 17.1% Black, 4.8% Hispanic, and 57.3% White. The Emergent Omicron cohort differed significantly from the Delta cohort in demographics, comorbidities, and socio-economic determinants of health. After propensity-score matching for demographics, socio-economic determinants of health, comorbidities, medications and vaccination status, the 3-day risks in the Emergent Omicron cohort outcomes were consistently less than half those in the Delta cohort: ED visit: 4.55% vs. 15.22% (risk ratio or RR: 0.30, 95% CI: 0.28-0.33); hospitalization: 1.75% vs. 3.95% (RR: 0.44, 95% CI: 0.38-0.52]); ICU admission: 0.26% vs. 0.78% (RR: 0.33, 95% CI:0.23-0.48); mechanical ventilation: 0.07% vs. 0.43% (RR: 0.16, 95% CI: 0.08-0.32). In children under 5 years old, the overall risks of ED visits and hospitalization in the Emergent Omicron cohort were 3.89% and 0.96% respectively, significantly lower than 21.01% and 2.65% in the matched Delta cohort (RR for ED visit: 0.19, 95% CI: 0.14-0.25; RR for hospitalization: 0.36, 95% CI: 0.19-0.68). Similar trends were observed for other pediatric age groups (5-11, 12-17 years), adults (18-64 years) and older adults (>= 65 years). Conclusions First time SARS-CoV-2 infections occurring at a time when the Omicron variant was rapidly spreading were associated with significantly less severe outcomes than first-time infections when the Delta variant predominated.

From Free Binding Energy Calculations of SARS-CoV-2—Receptor Interactions to Cellular Immune Responses

“…Reports of disease severity upon infections with SARS-CoV-2 Omicron, though at first anecdotal [38] or based on preliminary clinical studies [39][40][41], were validated by recent clinical studies from other parts of the world [42,43], confirming an overall less severe, rather mild, or even asymptomatic disease outcome, which again stands in agreement with results from in vitro studies [44] as well as with weaker binding of the virus to its receptor. Enhanced replication of SARS-CoV-2 Omicron in nasal epithelial cells has been shown and supports higher contagiousness whereas the reduced viral yields in human lung cells are in line with reduced disease severity [45].…”

Clinical outcomes associated with Omicron (B.1.1.529) variant and BA.1/BA.1.1 or BA.2 subvariant infection in southern California

“…Several studies have found similar reductions in severity with infection from Omicron compared to infection from other SARS-CoV-2 variants. In other settings, estimated reductions in risk of hospitalization with Omicron variant infection have ranged from 20-80% [9][10][11]22,23]. Variability in estimates between studies is likely in part due to different definitions of the primary endpoint (e.g.…”

Omicron SARS-CoV-2 Variant of Concern: A Review on its Transmissibility, Immune Evasion, Reinfection, and Severity

“…Although Omicron showed a greater ability to evade immunity developed by vaccinations and previous infections, we found signi cantly reduced severity in Omicron infections. Almost all the studies we reviewed consistently reported a considerably lower risk of requiring hospital admission, ICU, and mechanical ventilators, shorter median stay at the hospital, and lower mortality rates among Omicron infections compared to Delta and other variants [3], [9], [16]- [19]. Also, we found that though Omicron has a greater ability to escape immunity developed by vaccines, booster/third doses are still signi cantly effective in protecting from symptomatic Covid infections [16].…”

“…A retrospective cohort study (Omicron cohort and Delta cohort) was carried out using electronic health record (EHR) data from 577,938 rst-time SARS-CoV-2 infection patients in the United States [19]. After adjustment for demographics, socioeconomic determinants of health, comorbidities, medications, and immunization status, the 3-day risks in the Emergent Omicron cohort were consistently less than half of those in the Delta cohort: Emergency Department (ED) visit: 4.55% vs. 15.22% (risk ratio or RR: 0.30, 95% CI: 0.28-0.33); hospitalization: 1.75% vs. 3.95% (RR: 0.44, 95% CI: 0.38-0.52]); ICU admission: 0.26% vs. 0.78% (RR: 0.33, 95% CI:0.23-0.48); mechanical ventilation: 0.07% vs. 0.43% (RR: 0.16, 95% CI: 0.08-0.32) [19].…”