FRIDAY, Sept. 23, 2022 (HealthDay News) — An increased risk of blood clots persists nearly a year after contracting COVID-19, a large study shows.

Health records of 48 million unvaccinated adults in the UK suggest that the first wave of the pandemic in 2020 could have led to an extra 10,500 cases of heart attack, stroke and other blood complications of clots, such as deep vein thrombosis, in England and Wales only.

The risk of blood clots persists for at least 49 weeks after infection, research found.

“We showed that even people who were not hospitalized faced a higher risk of blood clots during the first wave,” said one of the study’s leaders, Angela Wood, deputy director of the British Heart Foundation’s Center for Data Science.

“While the risk to individuals remains small, the impact on population health could be substantial, and strategies to prevent vascular events will be essential as we move forward with the pandemic,” Wood said in a press release from Health Data Research UK, which sponsors the centre.

The researchers found that the risks decreased over time.

Patients were 21 times more likely to have a a heart attack or a stroke within a week of being diagnosed with COVID. After four weeks, the risk was 3.9 times greater than normal.

Heart attacks and strokes are mainly caused blood clots blocking arteries.

The risk of venous blood clots was 33 times greater within a week of being diagnosed with COVID, dropping to eight times four weeks later. Conditions caused by these clots include deep vein thrombosis and thromboembolism of the pulmonary arterywhich can be fatal.

The study found that 26 to 49 weeks after being diagnosed with COVID, the risk of clots in arteries decreased by 1.3 times and in veins by 1.8 times.

Although people who were not hospitalized had a lower risk, it was not zero, the study found.

Overall, the individual risk remains low, the authors note. Men over 80 years of age are most at risk.

“We are reassured that the risk is falling fairly quickly – especially for heart attacks and strokes – but that it remains elevated for some time highlights the long-term effects of COVID-19, which we are only beginning to understand,” said one of the study’s leaders. Jonathan Stern, Director, NIHR Bristol Biomedical Research Center and UK Health South West Data Research Unit.

The authors say that steps such as giving high-risk patients medication to lower blood pressure may help reduce the incidence of serious clots.

Researchers are now examining the new data to understand how vaccination and the impact of new COVID variants may affect the risk of blood clotting.

The findings were recently published in a journal Circulation.

Additional information

The US Centers for Disease Control and Prevention has more blood clots.

SOURCE: Health Data Research UK, press release, 20 September 2022

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