A study of the lungs of people who have died from COVID-19 has found persistent and extensive damage in most cases and may help doctors understand what is behind a syndrome known as 'long COVID'.
Scientists leading the research say they also found some unique characteristics of SARS-CoV-2, the virus that causes COVID-19, which may explain why it is able to inflict such harm.
"The findings indicate COVID-19 is not simply a disease caused by the death of virus-infected cells but is likely the consequence of these abnormal cells persisting for long periods inside the lungs," said King's College London professor Mauro Giacca.
Researchers analysed samples of tissue from the lungs, heart, liver and kidneys of 41 patients who died of COVID-19 at Italy's University Hospital of Trieste between February and April.
Giacca said while his team found no overt signs of viral infection or prolonged inflammation in other organs, they discovered "really vast destruction of the architecture of the lungs", with healthy tissue "almost completely substituted by scar tissue".
"It could very well be envisaged that one of the reasons why there are cases of long COVID is because there is vast destruction of lung (tissue)," he said.
"Even if someone recovers from COVID, the damage that is done could be massive."
Growing evidence suggests a small proportion of people who have had COVID-19 and recovered can experience a range of ongoing symptoms including fatigue, brain fog and shortness of breath.
The condition is known as long COVID.
Giacca said almost 90 per cent of the 41 patients had several characteristics unique to COVID-19 compared to other forms of pneumonia.
One was extensive blood clotting of the lung arteries and veins.
Another was that some lung cells were abnormally large and had many nuclei - a result of the fusion of different cells into single large cells in a process known as syncytia.
The research, published in the journal Lancet eBioMedicine, also found the virus was still present in many types of cells.