New coronavirus study reveals increased risks from middle age

Ian Sample Science editor
Photograph: Barcroft Media/Barcroft Media via Getty Images

The first comprehensive study of Covid-19 deaths and hospitalisations in mainland China has revealed in stark detail the increase in risk for coronavirus patients once they reach middle age.

The analysis found that while the overall death rate for confirmed cases was 1.38%, the rate rose sharply with age – from 0.0016% in the under 10s, to 7.8% in 80s and over.

The study showed only 0.04% of 10 to 19-year-olds required hospital care compared with more than 18% of those in their 80s and above.

Dramatic rises were seen among middle-aged groups too, with 4% of people in their 40s needing hospital treatment and more than 8% of patients in their 50s.

The estimates, reported in Lancet Infectious Diseases, are based on an analysis of 70,117 laboratory-confirmed and clinically-diagnosed cases in mainland China, combined with 689 positive cases among people evacuated from Wuhan on repatriation flights.

“Our estimates can be applied to any country to inform decisions around the best containment policies for Covid-19,” said Professor Azra Ghani, a co-author of the study.

“Our analysis very clearly shows that at aged 50 and over, hospitalisation is much more likely than in those under 50, and a greater proportion of cases are likely to be fatal.”

Because countries have taken radically different approaches to testing, and have sometimes changed testing strategies from one week to the next, scientists have struggled to compare death rates between countries. Another difficulty has been working out the proportion of people who die after becoming infected, because many cases are never confirmed. The latest study estimates the number of undetected cases arriving at an overall death rate of 0.66%. While the figure is lower than some recent estimates, it is markedly higher than the 2009 pandemic “swine flu” virus which killed about 0.02% of those infected.

The findings mirror the picture that has emerged around the world with the virus inflicting most harm on older people who tend to have more underlying health problems, such as medical conditions that weaken the lungs or heart.

The authors at Imperial College London, who are advising the UK government on the outbreak, warn that since half to 80% of the global population could be infected with Covid-19, the number of people needing hospital treatment is likely to overrun even the most modern healthcare services.

Professor Neil Ferguson, a senior author on the study, said that as the UK epidemic unfolds, similar proportions from each age group in the UK are likely to be hospitalised and die as seen in China.

Travel restrictions, social distancing and lockdowns across Britain and elsewhere are all intended to suppress transmission of coronavirus.

According to further modelling released on Monday by the Imperial College group, such measures will have a major impact in Europe if they are kept in place, averting an estimated 59,000 deaths in 11 European countries by the end of March.

Without sufficient testing to reveal how widespread the virus is, the group’s estimates vary substantially from 7 million to 43 million infected people across the 11 countries analysed as of 28 March. In the UK the infection rate is estimated at 2.7%.

The warning came as researchers in the US shed light on a crucial biological mechanism that has helped the coronavirus spread rapidly among humans around the world.

A detailed analysis of the virus’s structure revealed that its club-like “spikes” enable it to latch on to human cells about four times more strongly than the related Sars coronavirus which killed hundreds of people in a 2002 pandemic. This means that coronavirus particles that are inhaled through the nose or mouth have a high chance of attaching to cells in the upper respiratory tract, and that relatively few are needed to establish an infection.

A 3D map of the virus’s binding protein will now be used by scientists to hunt for drugs that can neutralise the virus before an infection takes hold. “If a new antibody drug can bind to those sites on the virus more strongly and frequently than the receptor, it will block the virus out of cells, making it a potentially effective treatment for viral infections,” said Fang Li, who led the study at the University of Minnesota. The work is published in Nature.