Thread by @sailorrooscout

A CWRU School of Medicine study of 577,938 pediatric and adult patients shows first time SARS-CoV-2 infections occurring at a time when Omicron was rapidly spreading were associated with significantly less severe outcomes than first time infections when Delta predominated. 🧵

It is IMPORTANT to note severity of disease in humans is NOT determined only by virus replication but also by the host immune response to the infection. Make sure you are PROTECTED. Source for the information above can be found here: medrxiv.org/content/10.110… PLEASE NOTE.

Currently, data on the severity of the disease caused by the Omicron variant compared with the Delta variant has been limited. Here, researchers compared 3-day risks of emergency department (ED) visit, hospitalization, intensive care unit (ICU) admission, & mechanical ventilation

in patients who were first infected during a time period when Omicron was emerging to those in patients who were first infected when Delta was predominant.

Researchers used electronic health record (EHR) data of 577,938 first-time SARS-CoV-2 infected patients from a multicenter, nationwide database in the U.S. 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

Omicron 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.

Of 14,054 patients in the Emergent Omicron cohort (average age, 36.4 ± 24.3 years), 27.7% were pediatric patients (<18 years old). 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).

Conclusion: First time SARS-CoV-2 infections occurring at a time when the Omicron variant was rapidly spreading were associated with significantly less severe outcomes and significantly milder disease than first-time infections when the Delta variant predominated.

Our findings of reduced hospitalization in the Emergent Omicron cohort compared to the Delta cohort is consistent with findings from Africa, Scotland, and England, that were based on genomic sequences, and goes further to indicate that the severity in hospitalization is reduced.

I recommend reading this thread in full as it looks into pediatric admissions, age stratified data, those with comorbidities, those on immunosuppressants, AND finally some data out of the US that falls in line with data out of several other countries.