Blood clot risk persisted for nearly a year after COVID-19 infection, study says

The risk of developing a blood clot remained elevated nearly a year after being infected with COVID-19, according to a new British study examining the medical records of 48 million unvaccinated adults, covering almost the entire adult English and Welsh population from the start year of the pandemic.

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

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

“We are reassured that the risk is falling fairly rapidly — particularly for heart attacks and strokes — but finding that it remains elevated for some time underscores the longer-term impact of COVID-19, which we are only just beginning to understand,” it said in the study co-lead Jonathan Sterne, 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 Swansea University, also found that the risk of vascular disease was “significantly higher” in the first week or two after COVID-19 was confirmed. 19, a risk that decreased over time. However, in contrast to (the risk of?) arterial thrombosis, which receded quickly after initial infection, VTE risks remained higher. The researchers found that the relative incidences of both arterial thrombosis and VTE remained high for longer, particularly in patients who were hospitalized.

Overall, the team found that patients were 21 times more likely to have artery-blocking clots, which can lead to heart attacks and strokes, within the first week of testing positive for COVID-19. That risk dropped to 1.3-fold sometime after six months. For VTE, the increased risks increased 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 risk of blood clots by age, the researchers found that black and Asian people and those with a history of blood clots were at higher risk compared to white patients. People with only mild or moderate COVID-19 cases were also affected, although their additional risk was generally lower than those with severe infections.

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

“While the risk to individuals remains low, the public health implications could be significant and strategies to prevent vascular events will be important as the pandemic progresses.”

The research team used anonymized electronic medical records for the entire English and Welsh population from 1 January to 7 December 2020 to analyze the data, including examining the severity of a patient’s COVID-19 infection, the patients’ demographics and their medical treatment history. The data collected would have predate the mass vaccination campaign and predate the dominance of variants such as Delta and Omicron.

“The large number of COVID-19 infections in England and Wales in 2020 and 2021 has likely resulted in a significant additional burden of arterial thrombosis and VTEs,” the paper’s authors wrote, recommending preventive strategies such as primary care health screening Physician and treatment of high-risk patients could help reduce the occurrence of dangerous blood clots. They found that the opposite occurred during the pandemic — fewer patients were seeing doctors, leading to fewer routine health checks for people with chronic medical conditions and fewer patient prescriptions for drugs that can help lower blood pressure and cholesterol.

The researchers noted some limitations of the study, including the fact that patients who died in nursing homes from a clot-related event may not have been recorded as such, for example due to a lack of diagnostic resources. Some people with 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 did not include information about certain milder forms of blood clots. In addition, the authors noted that testing for COVID-19 for mild or asymptomatic cases was not widely available in the early days of the pandemic.

Looking ahead, researchers are examining post-2020 data to better understand how vaccination and other variants affect vascular health.