Right at the beginning of the coronavirus pandemic, it became clear that elderly people were most at risk of dying from a result of infection.
But a mammoth new study of 17 million people has revealed there multiple other factors that put people in the firing line of Covid-19 – including race and social disadvantage.
Researchers from Oxford University in the United Kingdom developed a system to analyse the health records of 40 per cent of National Health Service patients, including 10,296 recorded coronavirus deaths.
As a result, they uncovered the risk factors that make the pandemic more likely to cause death, with the unprecedented findings released in the academic journal Nature.
"Covid-19 has rapidly affected mortality worldwide," the authors noted. "There is unprecedented urgency to understand who is most at risk of severe outcomes, requiring new approaches for timely analysis of large datasets."
When the World Health Organisation declared coronavirus a pandemic on March 11, 118,000 cases had been recorded across 114 countries, resulting in 4291 deaths.
Now, some 12.2 million have been infected and more than 552,000 people are dead.
Understanding what makes some patients much more likely to perish, while others experience only mild illness and recover, can help health authorities target their efforts to control the disease and protect the vulnerable.
This new study took the primary care records of 17.2 million Brits and pseudonymously linked them to almost 11,000 coronavirus-related deaths.
"Age and gender are well-established risk factors for severe Covid-19 outcomes, with over 90 per cent of UK deaths being in people over 60, and 60 per cent in men," the authors noted.
Males had a 1.59-fold higher risk of death from coronavirus than women, while people aged over 80 had a 20-fold increased risk compared to those aged 50 to 59.
But the Oxford research also uncovered a link between race and risk of coronavirus-related death.
Black and South Asian people, and those of mixed background, were 1.62 to 1.88 times more likely to die from Covid-19 than white people, after taking into account their prior medical conditions, the authors said.
People from the most deprived areas in the cohort were 1.8 times more likely to die from coronavirus than the least deprived.
The authors added that clinical factors made only a small contribution to this risk, suggesting that social factors play a role.
"The underlying causes of higher risk of Covid-19 death among those from non-white backgrounds, and deprived areas, require further exploration – we would suggest collecting data on occupational exposure and living conditions as first steps."
Pre-existing medical conditions, including obesity and particularly patients with a BMI of over 40, as well as diabetes, severe asthma, and respiratory, chronic heart, liver, neurological and auto-immune diseases, were all found to be associated with an increased risk of death.
A separate survey of 16,749 patients in the UK who were hospitalised with Covid-19 showed a higher risk of death for people with cardiac, pulmonary and kidney disease, as well as malignancy, dementia and obesity.
Analysis of coronavirus patients in both France and New York hospitals also found a link between obesity and an increase in required treatment for infection.
In their study, the authors offer a note of caution related to clinically suspected but unconfirmed cases of Covid-19, which were included in the dataset.
Some patients might have been incorrectly identified as having Covid-19 and, conversely, some deaths – particularly at earlier stages – might have been misclassified as non-Covid, they said.
In addition, the sample included only 17 per cent of GP clinics in London, which might not be fully representative of the population.
"The statistical power offered by our approach means that associations with less common risk factors can be robustly assessed in more detail, at the earliest possible date, as the pandemic progresses," they said.