Hospitalization trends and associated factors for COVID in 2.3 million adults in England

The case-fatality ratio (CFR) and case hospitalization ratio (CHR) of coronavirus disease 2019 (COVID-19) vary over time. Notably, the impact of the underlying risk of infected individuals on these ratios is still unknown.

Several studies have been conducted to characterize the risk factors associated with hospitalization and mortality in COVID-19 patients; however, they may not be representative of subsequent pandemic waves, along with the emergence of new variants.

Study: Trends and associated factors for Covid-19 hospitalisation and fatality risk in 2.3 million adults in England. Image Credit: Blue Planet Studio /

About the study

In a recent article published on the pre-print server medRxiv*, researchers from the United Kingdom performed a national level, retrospective cohort study with the primary aim of determining the risk factors for hospitalization and mortality rates over time among COVID-19 patients in England.

The secondary aim of this study was to identify patient characteristics associated with hospitalization and mortality risk. The researchers were also interested in evaluating whether residual unexplained variation in the CHR and CFR remains after accounting for differences in the underlying risk factors of those infected.

Individuals 18 years or older who tested positive for COVID-19 between October 1, 2020, and April 30, 2021, were included in the study. The data of the participants were linked with primary and secondary care electronic health records and death registrations.

The participants were monitored from the day of positive severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) test for up to 28 days. The two primary outcomes of this study included one or more emergency hospitalization and/or death within 28 days of follow-up for any reason.

A multivariable multilevel logistic regression model was used to evaluate each outcome with patient risk factors and time. Further, age- and time-specific CHR and CFR were determined for each outcome by calculating the predicted probability of the outcome within each age group and study week stratum.


A total of 2,311,282 individuals were included in the current study, among which 164,046 individuals were admitted to the hospital at least once during the complete study duration. This indicates a CHR of 7.1% and 53,156 deaths occurred within 28 days from a positive test, which indicates a CFR of 2.3%.

A significant elevation in hospitalization rates and mortality risk over time was observed from late December 2020 to early February 2021, which was consistent after individual risk factor adjustment. The peak in CHR was observed during January 2021 in age groups of 40 years and above and had consistently risen until April 2021.

The study found a higher risk of hospitalization and mortality in older individuals, males, people of Asian and Black ethnic backgrounds, and those living in more deprived areas. The study results also indicated a 10% greater risk of hospitalization and a 99% higher risk of mortality in underweight people, which may be due to unmeasured conditions like frailty. Individuals who were obese had a 93% greater risk of hospitalization but a 4% higher mortality risk as compared to individuals with a healthy weight.

The U.K. adopted a clinically extremely vulnerable (CEV) status for individuals at the highest risk of COVID-19-related mortality due to several risk factors such as increased age, male gender, and obesity. The study results indicated an 85% higher risk of hospitalization but a 12% lower risk of mortality in CEV patients after full adjustment of individual risk factors. Current smokers displayed a lower risk of hospitalization as compared to non-smokers but an increase in the risk of mortality after adjustment.

The study also found a strong association between chronic conditions such as chronic respiratory disease, hypertension, chronic kidney disease, dementia, learning disability, stroke, and diabetes, and hospitalization and deaths. However, this was not true for patients with dementia, who were associated with a 6% lower risk of hospitalization.


Overall, the study findings demonstrated that the risk of hospitalization and death from COVID-19 varied significantly during the second wave of the COVID-19 pandemic in England, independent of the underlying condition/risk in the infected individuals. People with individual risk factors such as older adults, males, those living in more deprived areas, and those with obesity had a higher risk of hospitalization and mortality. Learning disability and severe mental illness were associated with the highest risk of hospitalization and mortality, thus emphasizing the need for more care and research in these groups.

*Important notice

medRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.

Journal reference:
Susha Cheriyedath

Written by

Susha Cheriyedath

Susha has a Bachelor of Science (B.Sc.) degree in Chemistry and Master of Science (M.Sc) degree in Biochemistry from the University of Calicut, India. She always had a keen interest in medical and health science. As part of her masters degree, she specialized in Biochemistry, with an emphasis on Microbiology, Physiology, Biotechnology, and Nutrition. In her spare time, she loves to cook up a storm in the kitchen with her super-messy baking experiments.


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