Blood clots still a risk a year after Covid infection, researchers find

While long Covid is now a well-documented phenomenon, new research has revealed another long-term complication.

Your risk of developing a blood clot remains far higher than normal even a year after infection.

The study, led by the University of Bristol and published in academic journal Circulation, focused on health data of 48-million people in the public health system in the UK.

Of those, 1.4-million had been diagnosed with Covid and of those, 10,500 had developed blood clot-related problems.

According to the American Heart Association, which publishes Circulation, “as seen in previous studies, Covid was linked to a sharply increased risk of blood clot-related issues — including heart attack and stroke — immediately after diagnosis compared to people who never had Covid-19.”

But the new study found that risk remained higher for some problems “up to 49 weeks later”.

“At that point, the risk of deep vein thrombosis — clots that form in large veins — was nearly double in people who’d had Covid compared to those who had not,” say the researchers.

Taking established preventive medications and managing your risk factors is even more important now than it was before the pandemic.

Jonathan Sterne, the study’s senior author, said the findings reinforce the message that for people who have cardiovascular conditions, “taking established preventive medications and managing your risk factors is even more important now than it was before the pandemic”.

A study of this nature has not been done in SA, but in the early days of the pandemic here, clinicians began to notice a dramatic rise in blood clots.

At the time, researchers were pointing out that understanding Covid as only a respiratory disease was incorrect as it is also a cardiovascular one.

According to Prof Keertan Dheda, head of the Lung Institute at the University of Cape Town, blood clots had not only been seen “clinically” during the course of the pandemic (in the veins of the legs, abdomen, lungs and some arteries) but had also been “verified in post-mortem studies”, which had shown clots in the large blood vessels as well as in the small blood vessels of the skin and the lungs.

“This is a field of intensive research,” Dheda said, adding that Covid injures the cells that line blood vessels.

This causes a hyperinflammatory state which is made more dangerous by the patient lying immobile in a bed, thus causing excessive clots to form in the veins and sometimes arteries.

The new study shows, however, that the risk remains high even after a recovered patient returns to normal activity.

Prof Elvis Irusen, head of pulmonology at Stellenbosch University, said pneumonia had been the “commonest cause of death with Covid-19 patients” but that all infections, especially coronavirus, “also activate the clotting system of the blood” and this can cause “both bleeding and a blood clot [thrombus]”.

Previous studies had shown that patients with swine flu, and other “very sick patients with severe viral pneumonia and acute respiratory distress syndrome” who had been admitted to hospitals, were shown to have a 23-times increased risk for pulmonary embolism (when a blood clot from elsewhere in your body, like a vein in your leg, travels and lodges itself in the lung).