Catching Covid is associated with a fivefold increase in the risk of deep vein thrombosis (DVT) and a 33-fold increase in risk of a potentially fatal blood clot on the lung in the 30 days after becoming infected, data suggests.
The findings, published in the British Medical Journal on Thursday, could help explain a doubling in the incidence of, and deaths from, blood clots in England since the start of the pandemic compared with the same periods in 2018 and 2019.
They also help to put the very small increased risk of blood clots associated with Covid-19 vaccination into context. “The degree of complications associated with Covid-19 is much stronger and lasts for much longer than what we might be getting after vaccination,” said Dr Frederick Ho, a lecturer in public health at the University of Glasgow, who was not involved in the research.
“Even those people with mild symptoms who do not need to be hospitalised might have a small increase in the risk of [blood clots].”
Although previous research had suggested that catching Covid was associated with an increased risk of blood clots, it was unclear for how long this risk remained, and whether mild infections also increased people’s risk.
To address these uncertainties, Anne-Marie Fors Connolly at Umeå University in Sweden and her colleagues measured the risk of DVT, pulmonary embolism – a blood clot on the lung – and various types of bleeding, such as gastrointestinal bleeding or a burst blood vessel in the brain, in more than 1 million people with confirmed Covid infections and more than 4 million uninfected individuals.
Overall, they identified a 33-fold increase in the risk of pulmonary embolism, a fivefold increase in the risk of DVT and an almost twofold increase in the risk of bleeding in the 30 days after infection. People remained at increased risk of pulmonary embolism for six months after becoming infected, and for two and three months for bleeding and DVT.
Although the risks were highest in patients with more severe illness, even those with mild Covid had a threefold increased risk of DVT and a sevenfold increased risk of pulmonary embolism. No increased risk of bleeding was found in those who experienced mild infections.
“Pulmonary embolism can be fatal, so it is important to be aware [of this risk],” said Connolly. “If you suddenly find yourself short of breath, and it doesn’t pass, [and] you’ve been infected with the coronavirus, then it might be an idea to seek help, because we find this increased risk for up to six months.”
Ho said the results remained relevant even in the Omicron era, since current vaccines were highly effective against severe Covid but breakthrough infections were common, even after a third dose of a vaccine.
“Despite the potential for new variants of concern, most governments are removing restrictions and shifting their focus to determining how best to live with Covid. This study reminds us of the need to remain vigilant to the complications associated with even mild Sars-CoV-2 infection, including [blood clots].”
News
Scientists Discover a New Form of Ice That Shouldn’t Exist
Researchers at the European XFEL and DESY are investigating unusual forms of ice that can exist at room temperature when subjected to extreme pressure. Ice comes in many forms, even when made of nothing but water [...]
Nobel-winning, tiny ‘sponge crystals’ with an astonishing amount of inner space
The 2025 Nobel Prize in chemistry was awarded to Richard Robson, Susumu Kitagawa and Omar Yaghi on Oct. 8, 2025, for the development of metal-organic frameworks, or MOFs, which are tunable crystal structures with extremely [...]
Harnessing Green-Synthesized Nanoparticles for Water Purification
A new review reveals how plant- and microbe-derived nanoparticles can power next-gen water disinfection, delivering cleaner, safer water without the environmental cost of traditional treatments. A recent review published in Nanomaterials highlights the potential of green-synthesized nanomaterials (GSNMs) in [...]
Brainstem damage found to be behind long-lasting effects of severe Covid-19
Damage to the brainstem - the brain's 'control center' - is behind long-lasting physical and psychiatric effects of severe Covid-19 infection, a study suggests. Using ultra-high-resolution scanners that can see the living brain in [...]
CT scan changes over one year predict outcomes in fibrotic lung disease
Researchers at National Jewish Health have shown that subtle increases in lung scarring, detected by an artificial intelligence-based tool on CT scans taken one year apart, are associated with disease progression and survival in [...]
AI Spots Hidden Signs of Disease Before Symptoms Appear
Researchers suggest that examining the inner workings of cells more closely could help physicians detect diseases earlier and more accurately match patients with effective therapies. Researchers at McGill University have created an artificial intelligence tool capable of uncovering [...]
Breakthrough Blood Test Detects Head and Neck Cancer up to 10 Years Before Symptoms
Mass General Brigham’s HPV-DeepSeek test enables much earlier cancer detection through a blood sample, creating a new opportunity for screening HPV-related head and neck cancers. Human papillomavirus (HPV) is responsible for about 70% of [...]
Study of 86 chikungunya outbreaks reveals unpredictability in size and severity
The symptoms come on quickly—acute fever, followed by debilitating joint pain that can last for months. Though rarely fatal, the chikungunya virus, a mosquito-borne illness, can be particularly severe for high-risk individuals, including newborns and older [...]
Tiny Fat Messengers May Link Obesity to Alzheimer’s Plaque Buildup
Summary: A groundbreaking study reveals how obesity may drive Alzheimer’s disease through tiny messengers called extracellular vesicles released from fat tissue. These vesicles carry lipids that alter how quickly amyloid-β plaques form, a hallmark of [...]
Ozone exposure weakens lung function and reshapes the oral microbiome
Scientists reveal that short-term ozone inhalation doesn’t just harm the lungs; it reshapes the microbes in your mouth, with men facing the greatest risks. Ozone is a toxic environmental pollutant with wide-ranging effects on [...]
New study reveals molecular basis of Long COVID brain fog
Even though many years have passed since the start of the COVID-19 pandemic, the effects of infection with SARS-CoV-2 are not completely understood. This is especially true for Long COVID, a chronic condition that [...]
Scientists make huge Parkinson’s breakthrough as they discover ‘protein trigger’
Scientists have, for the first time, directly visualised the protein clusters in the brain believed to trigger Parkinson's disease, bringing them one step closer to potential treatments. Parkinson's is a progressive incurable neurological disorder [...]
Alpha amino acids’ stability may explain their role as early life’s protein building blocks
A new study from the Hebrew University of Jerusalem published in the Proceedings of the National Academy of Sciences sheds light on one of life's greatest mysteries: why biology is based on a very specific set [...]
3D bioprinting advances enable creation of artificial blood vessels with layered structures
To explore possible treatments for various diseases, either animal models or human cell cultures are usually used first; however, animal models do not always mimic human diseases well, and cultures are far removed [...]
Drinking less water daily spikes your stress hormone
Researchers discovered that people who don’t drink enough water react with sharper cortisol spikes during stressful events, explaining why poor hydration is tied to long-term health risks. A recent study in the Journal of Applied [...]
Nanomed Trials Surge Highlighting Need for Standardization
Researchers have identified over 4,000 nanomedical clinical trials in progress now, highlighting rapid growth in the field and the need for a standardized lexicon to support clinical translation and collaboration. Nanotechnology is the science of [...]
