People who have recovered from Covid-19, regardless of the severity of their disease, may be at risk of developing blood clots due to an overactive immune system, according to a study.
Blood clots in major arteries, especially those which are linked to vital organs, can increase a person's risk of heart attack, stroke or organ failure.
Blood samples from 30 patients who had recovered from mild, moderate and severe Covid-19 were collected a month after they had been discharged from the hospital.
All of them were found to have blood vessel damage, possibly arising from a lingering immune response, which could trigger the formation of blood clots.
Around half of the patients had pre-existing cardiovascular risks, such as diabetes and hypertension, which put them at higher risk of blood clotting, said Assistant Professor Christine Cheung from Nanyang Technological University's Lee Kong Chian School of Medicine on Tuesday (April 13).
Speaking at a virtual media briefing, she noted that these patients also had more pronounced blood vessel dysfunction compared with the group who had no cardiovascular risks.
Prof Cheung's colleague, research assistant Florence Chioh, who is the first author of the study, said that the Sars-CoV-2 virus may attack the linings of blood vessels, causing inflammation and damage. This could result in leakage from these damaged vessels, triggering the formation of blood clots, she added.
However, the researchers discovered that even after patients had recovered from Covid-19, they continued to have high levels of an inflammatory protein known as cytokines - which are produced by immune cells to activate an immune response against pathogens - even in the absence of the virus.
An unusually high number of immune cells, known as T-cells, were also present in the blood of recovered patients, thus suggesting that their immune response remains activated even after the virus is gone.
Patients who have recovered from Covid-19 often have virus-specific T-cells in their bloodstream, which give them some level of protection against the virus.
However, the heightened immune response could trigger the cytokines to attack the blood vessels, increasing the risk of blood clot formation.
