Half of hospitalised Covid patients develop at least one other serious health complication, a study by Sage scientists and Prof Jonathan Van Tam, the Deputy Chief Medical Officer, has found.
Data from the study, which has been running since March last year, has been shared with the Government throughout the pandemic.
The findings – published in The Lancet on Thursday – include information on more than 70,000 patients who were admitted to hospital in the UK during the first wave, before vaccines were available.
A majority of the patients would have had to fend off Covid without treatments, as dexamethasone, the first and most effective Covid drug, was not found to work until last June.
Half of the patients (36,367 of 73,197) in the study developed a further health complication while battling Covid. Kidney injury was the most common (24.3 per cent), followed by lung problems (18.4 per cent) and heart complications (12.3 per cent).
Those with complications were nearly twice as likely to die and seven times more likely to need intensive care when compared to people without them, the study found.
Data came from more than 300 hospitals in the UK and found that men and over-60s were the most likely to develop complications.
Course of major symptoms and outcomes from illness onset in patients hospitalised with COVID-19
However, the study authors said problems were also commonplace in younger, previously healthy adults.
The findings showed that 27 per cent of 19 to 29-year-olds and 37 per cent of 30 to 39-year-olds experienced a complication. These figures rise to 54 per cent of 60 to 69-year-olds and to 52 per cent for people in their 80s.
One in eight (13 per cent) of the youngest group, aged 19 to 29, suffered acute complications which meant they were unable to look after themselves after being discharged.
Prof Calum Semple, a consultant respiratory paediatrician in Liverpool and a member of Sage, was the chief investigator and joint senior author of the study.
"This work contradicts current narratives that Covid is only dangerous in people with existing comorbidities and the elderly," he said. "I was actually really quite surprised. I was expecting the same relationship that we saw with death, in other words that the complications would be those in the frail and the elderly.
"And I was really quite distraught to see that we were talking about young people, previously fit and well, having complications.
"Sure, young people will not die from this disease, but younger adults will be damaged by this disease and leave a legacy, which for the range of their lives could have a significant impact on what they want to do and how they want to live."
Fatigue was the most common symptom reported as part of individuals’ experience of long Covid
The researchers predict that Covid complications are likely to cause significant challenges for individuals and the health and social care system in the coming years.
Dr Thomas Drake, the study co-author, of the University of Edinburgh, said: "Our study shows it is important to consider not just death from Covid-19 but other complications as well. This should provide policymakers with data to help them make decisions about tackling the pandemic and planning for the future.
"We are still studying the participants in our study to understand the long-term effects of Covid-19 on their health."
Prof Van Tam said: "The ISARIC/CO-CIN study was set up at very short notice in March 2020. Ever since, it has delivered a steady stream of high-quality data to the UK’s Sage committee and the Department for Health and Social Care on patients hospitalised with SARS-CoV-2 infection.
"The project has also produced a series of highly important peer-reviewed science papers which have been heavily cited and are of benefit to scientists worldwide."