Transmissibility, hospitalization, and intensive care admissions due to omicron compared to delta variants of SARS-CoV-2 in Catalonia : A cohort study and ecological analysis
Català, Martí (University of Oxford. Nuffield Department of Orthopedics, Rheumatology and Musculoskeletal Sciences)
Coma, Ermengol (Institut Català de la Salut)
Alonso Muñoz, Sergio (Universitat Politècnica de Catalunya. Departament de Física)
Andrés, Cristina (Instituto de Salud Carlos III)
Blanco Guillermo, Ignacio (Institut Germans Trias i Pujol. Hospital Universitari Germans Trias i Pujol)
Antón, Andrés (Instituto de Salud Carlos III)
Bordoy, Antoni E. (Instituto de Salud Carlos III)
Cardona, Pere-Joan (Universitat Autònoma de Barcelona. Departament de Genètica i de Microbiologia)
Fina, Francesc (Institut Català de la Salut)
Martró, Elisa (Institut Germans Trias i Pujol. Hospital Universitari Germans Trias i Pujol)
Medina, Manuel (Institut Català de la Salut)
Mora, Núria (Institut Català de la Salut)
Saludes, Verónica (Institut Germans Trias i Pujol. Hospital Universitari Germans Trias i Pujol)
Prats, Clara (Universitat Politècnica de Catalunya. Departament de Física)
Prieto-Alhambra, Daniel (University of Oxford. Nuffield Department of Orthopedics, Rheumatology and Musculoskeletal Sciences)
Alvarez-Lacalle, Enrique (Universitat Politècnica de Catalunya. Departament de Física)

Data:	2022
Resum:	We aim to compare the severity of infections between omicron and delta variants in 609,352 SARS-CoV-2 positive cases using local hospitalization, vaccination, and variants data from the Catalan Health Care System (which covers around 7. 8 million people). We performed a substitution model to establish the increase in transmissibility of omicron using variant screening data from primary care practices (PCP) and hospital admissions. In addition, we used this data from PCP to establish the two periods when delta and omicron were, respectively, dominant (above 95% of cases). After that, we performed a population-based cohort analysis to calculate the rates of hospital and intensive care unit (ICU) admissions for both periods and to estimate reduction in severity. Rate ratios (RR) and 95% confidence intervals (95% CI) were calculated and stratified by age and vaccination status. In a second analysis, the differential substitution model in primary care vs. hospitals allowed us to obtain a population-level average change in severity. We have included 48,874 cases during the delta period and 560,658 during the omicron period. During the delta period, on average, 3. 8% of the detected cases required hospitalization for COVID-19. This percentage dropped to 0. 9% with omicron [RR of 0. 46 (95% CI: 0. 43 to 0. 49)]. For ICU admissions, it dropped from 0. 8 to 0. 1% [RR 0. 25 (95% CI: 0. 21 to 0. 28)]. The proportion of cases hospitalized or admitted to ICU was lower in the vaccinated groups, independently of the variant. Omicron was associated with a reduction in risk of admission to hospital and ICU in all age and vaccination status strata. The differential substitution models showed an average RR between 0. 19 and 0. 50. Both independent methods consistently show an important decrease in severity for omicron relative to delta. The systematic reduction happens regardless of age. The severity is also reduced for non-vaccinated and vaccinated groups, but it remains always higher in the non-vaccinated population. This suggests an overall reduction in severity, which could be intrinsic to the omicron variant. The fact is that the RR in ICU admission is systematically smaller than in hospitalization points in the same direction.
Ajuts:	"la Caixa" Foundation 100010434 Agencia Estatal de Investigación PGC2018-095456-B-I00
Drets:	Aquest document està subjecte a una llicència d'ús Creative Commons. Es permet la reproducció total o parcial, la distribució, la comunicació pública de l'obra i la creació d'obres derivades, fins i tot amb finalitats comercials, sempre i quan es reconegui l'autoria de l'obra original.
Llengua:	Anglès
Document:	Article ; recerca ; Versió publicada
Matèria:	COVID-19 ; Severity ; Ecological study ; Cohorts ; Substitution model ; Severity and vaccination status
Publicat a:	Frontiers in Public Health, Vol. 10 (August 2022) , ISSN 2296-2565

DOI: 10.3389/fpubh.2022.961030
PMID: 36033822

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