A Swedish study published in the British Medical Journal in February shows that the risk of developing deep vein thrombosis or blood clots increases significantly after being infected with Covid-19, even several months after infection. Previous studies had identified this risk but had not analyzed its duration or its relationship to the severity of the infection.

To reach these conclusions, the Swedish researchers calculated the rate of venous thrombosis, pulmonary embolism and bleeding in four million uninfected people and one million infected people.

The study found that there is an increased risk of deep vein thrombosis, a clot in the leg, for up to three months after infection, pulmonary embolism, a clot in the lungs, for up to six months, and bleeding events for up to two months.

This study also shows that a Covid-19 infection increases the risk of deep thrombosis by a factor of five and the risk of developing pulmonary blood clots up to and including death within 30 days of infection by a factor of thirty-three.

The risks are higher in subjects with severe disease or some form of comorbidity, but they also exist in patients with a mild form of Covid-19, with about three times the probability of developing deep vein thrombosis and seven times the probability of developing pulmonary embolism.

The results also showed a higher risk in the first wave than in the second and third waves, so the researchers believe that vaccination may have reduced the risk after the first wave. However, because the study was conducted on people infected between February 2020 and May 2021, it is not possible to know whether the same risks persist with the Omicron variant.

An editorial in the British medical journal states that this study could explain why the number of deaths due to blood clots has doubled in the UK since the beginning of the pandemic.

Another interest of this study is to alert the need for vigilance against complications related to Covid-19 infection such as thrombosis and embolisms, while at the same time most governments are lifting restrictions and favouring living with the virus.

The study authors say that vaccination decreases both the risk of infection and severe symptoms but also the risk of developing a blood clot or deep vein thrombosis.

Already, in August 2021, a British study had shown that the risk of developing a venous thrombosis of the phlebitis type was two hundred times higher by being infected with Covid-19 than by being vaccinated with the AstraZeneca vaccine and that the risk of developing a stroke was eleven times higher in infected people than in vaccinated people.

https://ici.radio-canada.ca/nouvelle/1874907/thrombose-caillots-risque-infection-covid-coronavirus