SINGAPORE - 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 by local scientists. 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.