The study,as per the Lancet medical journal, included more than 70,000 adults in the UK admitted to hospital with severe Covid-19 disease.
Of these, half (36,367 of 73,197) developed one or more health complications during their stay.
Kidney injury was the most common complication (24.3%), followed by lung complications (18.4%) and heart complications (12.3%).
According to the study, 27% of 19 to 29-year-olds and 37% of 30 to 39-year-olds experienced a complication.
Acute complications were associated with reduced ability self-care discharge – with 13% of 19 to 29-year-olds and 17% of 30 to 39-year-olds unable to look after themselves once discharged from hospital.
Chief investigator and joint senior author of the study, Professor Calum Semple, from the University of Liverpool, said: “This work contradicts current narratives that Covid-19 is only dangerous in people with existing comorbidities and the elderly.
“Dispelling and contributing to the scientific debate around such narratives has become increasingly important.
“Disease severity at admission is a predictor of complications even in younger adults, so prevention of complications requires a primary prevention strategy, meaning vaccination.”
He told a press briefing: “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.
Prof Semple added: “My personal position and where this would influence my advice on the policy, is the message around Covid being a disease of the frail and the elderly and the young have got nothing to worry about.
“We now realise that paradigm is naive – 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.”
Overall, complications occurred in 50% of all participants, including in 44% (21,784 of 50,105) of participants who survived