The study indicates that the risk of developing blood clots remains for about a year after infection with the COVID-19 virus

Newswise — COVID-19 infection increases the risk of potentially life-threatening blood clots for at least 49 weeks, according to a new study of the health records of 48 million adults who were not immunized from the first wave of the pandemic.

The findings suggest that the COVID-19 pandemic may have resulted in an additional 10,500 cases of heart attacks, strokes and other thrombotic complications such as DVT in England and Wales in 2020 alone, although the increased risk to individuals remains small and diminishes. over time.

The research – which involved a large team of researchers led by the universities of Bristol, Cambridge, Edinburgh and Swansea University – shows that only people with mild or moderate disease are affected as well. The authors suggest that preventive strategies, such as giving high-risk patients drugs to lower blood pressure, can help reduce the incidence of serious thromboembolism.

Researchers studied de-identified electronic health records across all residents of England and Wales from January to December 2020 to compare the risk of blood clots after COVID-19 with risks at other times. The data was accessed securely and securely via the NHS Digital Trusted Research Environment in England, and the SAIL Data Bank in Wales.

In the first week after COVID-19 was diagnosed, people were 21 times more likely to have a heart attack or stroke, conditions mainly caused by blood clots blocking arteries. This decreased to 3.9 times more likely after 4 weeks.

Researchers have also studied conditions caused by blood clots in the veins: These include deep venous thrombosis and pulmonary embolism – a clot in the lungs that can be fatal. The risk of blood clots in the veins was 33 times greater in the first week after the diagnosis of COVID-19. This decreased to eight times the risk after four weeks.

The greatest risk of blood clots after COVID-19 remained for the duration of the study, although at 26 to 49 weeks, it decreased to 1.3 times more likely to have clots in the arteries and 1.8 times more likely to have clots in the veins.

Most previous research has examined the effect of COVID-19 on blood clotting in people hospitalized with COVID-19. The new study shows that there was also an effect in people who were not hospitalized with COVID-19, although their increased risk was not as great as those who were severely ill and hospitalized.

The authors say that individuals’ risk of blood clots remains low. In those most at risk — men over 80 — an additional 2 out of every 100 men who have had a stroke or heart attack after contracting COVID-19 infection may develop.

The data analyzed was collected in 2020, before the launch of mass vaccination in the UK, and before the spread of the newest types of COVID-19 such as Delta and Omicron. Researchers are now studying data beyond 2020 to understand the impact of vaccination and the impact of newer variables.

Publish the research in the journal Rotation It was supported by the BHF Data Science Center at Health Data Research UK, the National COVID-19 Health and Welfare National Baseline Study, the National Data and Communication Core Study, and the COVID-19 Long CONVALESCENCE Study.

Jonathan Stern, Professor of Medical Statistics and Epidemiology at the University of Bristol, Director of the National Institute of Human Rights’ Bristol Biomedical Research Center and Director of Health Data Research UK South West, who co-led the study, said: “We are reassured that risks are declining very rapidly. — particularly for heart attacks and strokes — but finding that it has remained elevated for some time highlights the long-term effects of COVID-19 that we are only just beginning to understand.”

Angela Wood, professor of biostatistics at the University of Cambridge, associate director of the British Heart Foundation Data Science Center, and co-leader of the study said: “We showed that even people who were not hospitalized had a higher risk of developing blood clots in the first wave. While the risks for individuals Still small, the impact on public health could be significant, and strategies to prevent vascular events will be important as we continue through the pandemic.”

Dr William Whiteley, a clinical epidemiologist and neurologist at the University of Edinburgh, who co-led the study, said: “The impact of MERS-CoV infection on the risk of blood clot-related conditions has not been well studied, and evidence-based methods for preventing these conditions after infection will be key to reducing Effects of the epidemic on patients.


Association of COVID-19 with major venous and arterial thrombotic diseases: a cohort population-level study of 48 million adults in England and Wales.Written by Jonathan A.C. Stern et al. in Rotation [open access]