COVID-19 AvonCAP Study

Researchers assessed whether Delta SARS-CoV-2 infection resulted in worse patient outcomes than Omicron SARS-CoV-2 infection, in hospitalised patients

The study, published in The Lancet Regional Health – Europe, 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.

Dr Catherine Hyams, Post-Doctoral Clinical Research Fellow, Principal Investigator for the AvonCAP study and one of the study’s lead authors at the University of Bristol, said: "By finding out the reduced requirement of increased oxygen support and total positive pressure support, including non-invasive ventilation, our analysis should contribute to future hospital care and service planning assessments. 

"However, the impact of lower severity Omicron-related hospitalisation must be balanced with increased transmissibility and overall higher numbers of infections with this variant."

The research team suggest there should be ongoing evaluation of the severity of new variants of SARS-CoV-2, along with careful planning of healthcare resource to avoid healthcare systems being overwhelmed.

Dr Leon Danon, Associate Professor in Infectious Disease Modelling and Data Analytics, in the Department of Engineering Mathematics and one of the study's lead authors, added: "These results have been published at a time when China is experiencing a resurgence of COVID-19 and may be useful in helping to understand what is happening there."

This research, published in The Lancet Regional Health – Europe, provides the first estimates of two- or three-dose Pfizer-BioNTech COVID vaccine effectiveness against hospital admission for more than three days and against respiratory difficulty requiring oxygen or ventilatory support.

Many studies have reported the effectiveness of the COVID-19 mRNA vaccines against hospitalisation, but few have assessed the effectiveness against clinically relevant measures of COVID-19 severity. Using detailed clinical data from Bristol’s two acute hospital Trusts, NBT and UHBW, researchers estimate the effectiveness of two- or three-doses of the (original/monovalent) Pfizer-BioNTech vaccine against hospitalisation for infection with either Delta or Omicron SARS-CoV-2 variants.

The study showed that receipt of two-doses of Pfizer-BioNTech vaccine may result in an 83% reduction in the rate of hospitalisation due to Delta SARS-CoV-2 infection, compared to the unvaccinated. Two doses also prevented severe in-hospital outcomes due to Delta SARS-CoV-2 infection, reducing the likelihood of a hospital admission lasting more than three days by 63%.  The researchers also found that two doses of this vaccine reduced the risk of a patient needing increased oxygen or ventilatory support by 52% and 59%, respectively.

Receipt of three-doses of Pfizer-BioNTech vaccine was also found to be effective in reducing Omicron infection severity, compared to the unvaccinated, including in older adults, reducing the risk of hospitalisation for more than three days with Omicron SARS-CoV-2 by 56%, and decreasing the risk of needing high-level oxygen or ventilatory support by 42% and 59%, respectively. This is additional evidence that Pfizer-BioNTech vaccine is effective in reducing hospital admissions due to Delta and Omicron SARS-CoV-2 infection.

Dr Anastasia Chatzilena, Postdoctoral Research Associate in the Department of Engineering Mathematics, and a lead author of the study, said: "Our research has shown the Pfizer-BioNTech vaccine provides effective protection against hospitalisation from Delta and Omicron infection and has significant benefits in terms of preventing severe disease, including critical care admission and respiratory failure.

"However, the benefit provided by vaccination decreases over time which appears to be more pronounced in older adults, so careful ongoing monitoring of vaccine effectiveness and SARS-CoV-2 disease severity for emerging variants remain important."

An increase in the number of non-COVID-19 respiratory infections should be expected this winter, say scientists. The warning comes following the results of a new study, published in The Lancet Regional Health – Europe, which found that over 55% of respiratory disease hospitalisations during the pandemic’s peak were caused by non-SARS-CoV-2 infections.

The study is the first to compare the number of hospitalisations from respiratory disease infections caused by COVID-19 and non-SARS-CoV-2 infections.  

Using data from 135,014 hospitalisations from two large hospitals in Bristol between August 2020 and November 2021, researchers identified 12,557 admissions attributable to acute Lower Respiratory Tract Disease (aLRTD) with patients admitted with signs or symptoms of respiratory infections including cough, fever, pleurisy, or a clinical or radiological aLRTD diagnosis. Of these, 12,248 (98%) patients, comprising mainly older adults, consented to participate in the study.

Following further analysis, the team show that of the 12,248 aLRTD hospitalisations, 55% (6,909) were due to infection with no evidence of SARS-CoV-2, while confirmed SARS-CoV-2 infection only accounted for 26% (3,178) of respiratory infections. The remaining 17% (2,161) were due to infection with no infective cause.