COVID: Risk of blood clots even higher one year after infection, study says

The risk of developing a blood clot remained elevated for nearly a year after a COVID-19 infection, according to a new UK study that looked at the health records of 48 million unvaccinated adults, covering nearly the entire adult English and Welsh population. , from the first year of the pandemic.

In a peer-reviewed paper published by the American Heart Association’s journal Circulation, researchers estimated that COVID-19 resulted in more than 10,500 additional heart attacks, strokes and other blood clot-related events in England and Wales by 2020. Although the excess risks were generally small and decreased over time, researchers still found that the chances of developing a venous thromboembolism (VTE) after a COVID-19 diagnosis up to 49 weeks after a positive test remained nearly twice as high, compared with people who were not diagnosed with the viral infection.

VTEs are blood clots in the veins, which, according to the U.S. Centers for Disease Control and Prevention, is a serious and underdiagnosed but preventable condition that can cause disability and death. A clot in the lung is an example of VTE. Arterial thrombosis is a clot that develops in an artery and is also potentially dangerous.

“We’re reassured that the risk is dropping quite quickly — particularly for heart attacks and strokes — but the finding that it remains elevated for a while highlights the long-term effects of COVID-19 that we’re only now beginning to understand,” the study said. co-lead, Jonathan Sterne, a professor of medical statistics and epidemiology at the University of Bristol, in a statement. Sterne is also Director of the NIHR Bristol Biomedical Research Center and Director of Health Data Research UK South West.

Like previous studies on blood clots, the team led by the Universities of Bristol, Cambridge and Edinburgh, and the University of Swansea also found that the risks of developing vascular disease were “significantly higher” in the first one to two weeks after confirmation. of COVID-19, a risk that decreased over time. However, in contrast to (the risk of?) arterial thrombosis, which decreased rapidly after the first infection, the VTE risks remained higher. However, the researchers found that the relative incidence of both arterial thrombosis and VTE remained higher for longer, especially in hospitalized patients.

Overall, the team found that within the first week of testing positive for COVID-19, patients were 21 times more likely to have artery-blocking blood clots, which can lead to heart attacks and strokes. This risk dropped to 1.3 times more likely sometime after six months. For VTE, the increased risk went from 33 times more likely in the first week to 1.8 times between 27 and 49 weeks.

While there was little association between COVID-19 and the risk of blood clots by age, researchers found that black and Asian people, and those with a history of blood clots, were at a higher risk compared to patients who were white. Those with only mild or moderate cases of COVID-19 were also affected, although their additional risk was generally lower than those with serious infections.

“We showed that even people who were not hospitalized were at a higher risk of blood clots in the first wave,” said Angela Wood, a professor of biostatistics at the University of Cambridge and co-leader of the study.

“While the risk to individuals remains small, the impact on public health could be significant and strategies to prevent vascular events will be important during the pandemic.”

The research team used anonymized electronic health records from the entire English and Welsh population from January 1 to December 7, 2020 to analyze the data, including looking at the severity of a patient’s COVID-19 infection, the patient’s demographics and their medical history. The data collected would have predate the mass vaccination campaign and before variants like Delta and Omicron became dominant.

“The high number of COVID-19 infections in England and Wales in 2020 and 2021 is likely to have led to a substantial additional burden of arterial thrombosis and VTEs,” the paper’s authors wrote, recommending preventive strategies such as a health assessment with a primary care physician and treating high-risk patients can help reduce the incidence of dangerous blood clots. They noted that the opposite happened during the pandemic — fewer patients saw doctors, leading to fewer routine health checks for people with chronic medical problems and fewer patient prescriptions for drugs that can help lower blood pressure and cholesterol.

Researchers noted some limitations to the study, including the fact that patients who died in nursing homes from a blood clot-related event may not have been registered as such, for example, due to a lack of diagnostic resources. Some people who experience milder cases of blood clotting may also have avoided going to the doctor or hospital because of concerns about contracting COVID-19. The data collected also does not include information about certain milder forms of clots. In addition, the authors noted that testing for COVID-19 was not widely available for mild or asymptomatic cases during the early days of the pandemic.

Looking ahead, researchers are studying data from after 2020 to better understand how vaccinations and other variants affect vascular health.

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