People with severe Covid-19 had a 1.6-1.9 times higher risk of developing a deep vein thrombosis or pulmonary embolism than people with severe influenza. This is apparent from a retrospective study based on US insurance data of 93,906 hospitalizations caused by these viruses (JAMA. 2022;328:637-51).
Based on clinical observations, during the first phase of the Covid-19 pandemic, the idea quickly emerged that the virus could be associated with an increased risk of thrombosis. It is now clear that the virus can infect endothelial cells and in this way fuel inflammation and disrupt clotting. However, it was unclear whether the virus actually differed from other viral agents in terms of absolute risks.
Using insurance data, an American research group now makes it plausible that the chance of developing a clinically significant venous thrombosis within 90 days is indeed at least 1.6 times higher in people who end up in hospital with Covid-19 than in hospital admissions. with influenza. They found no significant difference for the risk of arterial occlusions.
They saw the increased risk of a pulmonary embolism or a deep vein thrombosis in admissions both during the time vaccines were on the market and before. The percentage of patients who received a venous occlusion was 9.5% for the first vaccines and 10.9% after that, versus 5.3% for those who were admitted to influenza during the 2018-2019 flu season.
It is nice that this study mirrors the results of a publication in JAMA Ophthalmology of last April (2022;140:523-7), in which a comparable study of 432,515 insured persons showed that Covid-19 was associated with an increased risk of retinal vein occlusions, while this was not true for arterial occlusions in the retina either. This suggests that the increased risk of thrombosis does not only apply to large veins, but possibly also to the smallest veins in the rest of the body.