Risk of serious blood clot events spike in the months after COVID-19
New observational research out of Sweden has tracked more than one million COVID-19 cases for months after their acute illness in order to determine how the disease influences subsequent risk of blood clots. The findings indicate COVID-19 significantly increases a person’s risk of deep vein thrombosis and pulmonary embolism in the months after infection.
The large study, published in The BMJ, looked at health data from 1,057,174 positive COVID-19 cases. This covers every single positive recorded case in Sweden from the beginning of the pandemic up to May 2021. A control group of four million age- and sex-matched subjects not positive with COVID was generated to quantify the increase in risk for blood clots caused by infection.
In the 30 days after an initial COVID-19 diagnosis the researchers found a 33-fold increase in pulmonary embolism risk, a five-fold increase in deep vein thrombosis (DVT) risk and a two-fold increase in general bleeding events. The heightened risk, compared to the uninfected control group, persisted 60 days for bleeding, 90 days for DVT, and 180 days for pulmonary embolism.
Factoring in acute disease severity, the researchers found those initially hit hardest with COVID-19 did experience greater long-term risk for blood clotting events. However, the increased risk was not zero in those experiencing mild COVID. Those with only a mild infection still showed a three-fold risk of DVT and a seven-fold risk of pulmonary embolism.
While this new study is the most robust to investigate the relationship between blood clots and SARS-CoV-2 infection it is not the first to identify this association. A large UK study last year found similar signs when it compared rates of hematological and vascular events after COVID-19 to rates of those same events after COVID vaccination.
That study more generally found significant increases in rates of stroke, heart attack and blood clotting a month after a COVID infection. It also found these rates of adverse events were much higher after COVID-19 than after vaccination, validating the suggestion that the deleterious after-effects of COVID-19 are much more impactful than any potential harms caused by vaccination.
Another UK study published last year found incidences of and deaths from thromboembolism doubled in the first six months of the pandemic compared to rates seen in the years prior.
Ioannis Katsoularis, an author on the new Swedish study from Ume? University, said the findings affirm the value of vaccination in reducing the likelihood and severity of COVID-19.