New Algorithm Identifies Vaccinated Groups at Highest Risk of COVID-19 Hospitalization and Death

Using a risk calculator, researchers have reported on findings on vaccinated people who are at greatest risk from severe COVID-19 leading to hospitalization or death from 14 days post the second dose vaccination, when substantial immunity should be expected.

The QCovid tool developed in 2020 by researchers from the University of Oxford (Oxford, UK) was updated by adding 1.5 million people in February 2021 to the list of those advised to shield, allowing them to identify groups more at risk of hospitalization or death from COVID-19. The researchers used UK’s national linked datasets from general practice, national immunization and SARS-CoV-2 testing, death registry and hospital episode data, in order to analyze a sample of over 6.9 million vaccinated adults, of whom 5.2 million had both vaccines doses, which was representative of the country’s population as a whole. This sample included 2,031 COVID-19 deaths and 1,929 COVID-19 related hospital admissions, of which 81 deaths and 71 admissions occurred 14 or more days after the second vaccine dose.


Based on this, the researchers have developed cumulative risk scores to calculate people’s risk of hospitalization or death from COVID-19 following one, or two vaccination doses. These scores take into account factors including age, sex, ethnic group and the background rate of COVID-19 infections, and in particular highlight an elevated risk to those who are immunosuppressed as a result of chemotherapy, a recent bone marrow or solid organ transplant, or HIV/AIDS; people with neurological disorders, including dementia and Parkinson’s; and care home residents, and those with chronic disorders including Down’s Syndrome.

The researchers have reported that there were relatively few COVID-19 related hospitalizations or deaths in the group who had received the second dose of any vaccine, meaning that the study lacked the statistical power to determine if the groups listed above are more, or less, at risk following a second vaccine dose compared with following the first dose. Furthermore, they did not distinguish between type of vaccination offered, and acknowledge that their study may have been limited by factors such as exposure, as occupation for example is not something that is often recorded in general practice or hospital records. The researchers hope that these data can be used in a variety of health and care settings to inform those more likely to be at risk, and potentially help to prioritize those identified for further trials of vaccines, boosters or future preventative therapies.

“This enormous national study of over five million people vaccinated with two doses across the UK has found that a small minority of people remain at risk of COVID-19 hospitalization and death. Our risk calculator helps to identify those who remain most at-risk post-vaccination,” said Aziz Sheikh, Professor of Primary Care Research & Development and Director of the Usher Institute at The University of Edinburgh. “Our new QCovid tool, developed with the help of experts from across the UK, has been designed to identify those at high risk who may benefit from interventions such as vaccine booster doses or new treatments such as monoclonal antibodies, which can help reduce the risk of progression SARS-CoV-2 infection to serious Covid-19 outcomes.”

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The Hong Kong Polytechnic University