Vascular disease in COVID-19 is not caused by a viral infection of blood vessels as the SARS-CoV-2 virus does not infect the channels of blood distribution in the body, researchers have found.

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COVID infection is known to increase the severe risk of blood clot in patients and cause cardiovascular complications. But researchers from the University of Queensland (UQ) found that the complications of COVID-19 are triggered by inflammation caused by infected airway cells, and not blood vessels, as previously thought. "At least 40 per cent of patients that are hospitalised with COVID-19 are at high risk of blood clots, and anticoagulation therapies are now being routinely used," said Emma Gordon from UQ's Institute for Molecular Bioscience.

"There have been many studies attempting to prove whether the virus is infecting cells of the inner blood vessel wall or not. By conducting our experiments using real, infectious viruses rather than fragments of the virus's spike protein, we can definitively say it is not," she added.

The study, published in Clinical and translational Immunology, helps clarify a key debate about the relationship between the virus and the lining of the blood vessels. Using sophisticated microscopy facilities, the researchers tracked where the virus travelled in the cells and visualised how blood vessels respond to the live virus.

According to immunologist Larisa Labzin, from the varsity, the body's inflammatory response had a big effect on the cardiovascular system because they work together to fight infection -- the blood delivers the immune cells to the site of infection and makes blood clots if the blood vessel is damaged.

"When our immune system works well, it clears the virus from our bodies. But sometimes it goes into overdrive and we get an overblown inflammatory response causing complications -- in the case of Covid-19, this is often blood clots, when there shouldn't be any," Labzin said.

"Knowing that it is inflammation causing these cardiovascular complications arising from COVID-19 rather than the virus itself will help us develop the right treatments, and a better understanding of how and why these complications arise," Labzin said.