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Studies find Omicron related hospitalisations lower in severity than Delta and Pfizer-BioNTech COVID vaccine remains effective in preventing hospitalisations

12 December 2022

Adult hospitalisations from Omicron-related SARS-CoV-2 (COVID-19) were less severe than Delta and the Pfizer-BioNTech vaccine (also known as Comirnaty and BNT162b2*) remains effective in preventing not only hospitalisation, but severe patient outcomes associated with COVID-19, two new research studies have found.

The University of Bristol-led research, funded and conducted in collaboration with Pfizer Inc., as part of AvonCAP, is published in The Lancet Regional Health – Europe.  

AvonCAP records adults who are admitted to Bristol’s two hospital Trusts – North Bristol NHS Trust (NBT) and University Hospitals Bristol and Weston NHS Foundation Trust (UHBW) with possible respiratory infection.

In the first paper ‘Severity of Omicron (B.1.1.529) and Delta (B.1.617.2) SARS-CoV-2 infection among hospitalised adults: a prospective cohort study in Bristol, United Kingdom’  researchers assessed whether Delta SARS-CoV-2 infection resulted in worse patient outcomes than  Omicron SARS-CoV-2 infection, in hospitalised patients   

The study aimed to provide more detailed data on patient outcomes, such as the need for respiratory support.

The research demonstrated that Omicron infection resulted in less serious outcomes than Delta in hospitalised patients. Compared to Delta, Omicron-related SARS-CoV-2 hospitalisations were 58% less likely to need a high level of oxygen support, 67% less likely to need ventilatory support (such as a ventilator) or more critical care, and 16% less likely to have a hospital admission which lasted for more than three days.

Read the University of Bristol press release

'Severity of Omicron (B.1.1.529) and Delta (B.1.617.2) SARS-CoV-2 infection among hospitalised adults: a prospective cohort study in Bristol, United Kingdom' by Dr Catherine Hyams, Dr Rob Challen, Professor Adam Finn et al. in The Lancet Regional Health – Europe [open access]

'Effectiveness of BNT162b2 COVID-19 vaccination in prevention of hospitalisations and severe disease in adults with SARS-CoV-2 Delta (B.1.617.2) and Omicron (B.1.1.529) variant between June 2021 and July 2022: a prospective test negative case-control study' by Dr Anastasia Chatzilena, Dr Catherine Hyams, Dr Rob Challen, Dr Leon Danon et al. in The Lancet Regional Health – Europe [open access]

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