People who have had Covid-19 have an increased risk of developing serious blood clots for up to six months after getting infected, even in mild cases, a study said.

Previous research has indicated that Covid raises the risk of blood clots, but the new study in the BMJ medical journal shows how long the threat can linger, AFP reports.

To find out, researchers compared data from more than a million people in Sweden's national registries who contracted Covid from February 2020 to May 2021, with a control groups of over four million who did not test positive.

They found that those with Covid had a higher risk of pulmonary embolism, a blood clot that blocks arteries in lungs, up to six months after infection.