Study findings updated . AI-assisted evidence summary, not individual medical advice or a clinician endorsement.
THE SHORT VERSION
What’s worth knowing.
The key findings, what they mean, and the context that matters.
THE HEADLINE TAKEAWAYRaised up to 49 weeksVein-clot and stroke rates stayed above normal through week 49 after COVID-19
Vein-clot and stroke risk spiked after COVID-19 and lingered almost a year.
In England and Wales, adults diagnosed with COVID-19 had 33.2 times the rate of a first vein clot in week 1 compared with people without a COVID-19 diagnosis, and 28.1 times the rate of ischemic stroke. In weeks 27 to 49, those rates were still 1.80 and 1.62 times higher. By week 49, the estimated extra risk was 0.25 percentage points for vein clots and 0.5 points for artery clots.
The first weeks after diagnosis carried by far the most danger, but the extra risk of clots and strokes faded slowly over the following months rather than ending with the illness. Observational study of 2020 records comparing rates (hazard ratios) with people without a COVID-19 diagnosis; it shows a link, not proof of cause.
See the evidence
Population-wide health-record study of about 48 million adults in England and Wales, following COVID-19 diagnoses made from January to December 2020.
From the study: “Adjusted hazard ratios for first VTE after COVID-19 diagnosis declined from 33.2 (95% CI, 31.3-35.2) in week 1 to 1.80 (95% CI, 1.50-2.17) during weeks 27 to 49.”
Raised up to 49 weeks
Knight R et al. Association of COVID-19 With Major Arterial and Venous Thrombotic Diseases: A Population-Wide Cohort Study of 48 Million Adults in England and Wales. Circulation. 2022.
From the study: “aHRs for ischemic stroke were higher than for MI: they declined from 28.1 (26.8–29.4) in week 1 to 1.62 (1.42–1.86) in weeks 27 to 49”
Raised up to 49 weeks
Knight R et al. Association of COVID-19 With Major Arterial and Venous Thrombotic Diseases: A Population-Wide Cohort Study of 48 Million Adults in England and Wales. Circulation. 2022.
From the study: “The estimated whole-population increases in risk of arterial thromboses and VTEs 49 weeks after COVID-19 diagnosis were 0.5% and 0.25%, respectively”
Raised up to 49 weeks
Knight R et al. Association of COVID-19 With Major Arterial and Venous Thrombotic Diseases: A Population-Wide Cohort Study of 48 Million Adults in England and Wales. Circulation. 2022.
Late-Omicron COVID-19 showed no sign of extra clot risk over other infections.
Late Omicron: 1.0× oddsOdds ratio, vein clot within a month, vs other respiratory infections, May 2022–Nov 2024
Across the whole pandemic, US adults with COVID-19 had 1.45 times the odds of a vein clot in the legs or lungs within a month compared with adults who had other acute respiratory infections. But in the later Omicron period (May 2022–Nov 2024), the odds ratio was 1.01, meaning no sign of extra risk.
For most adults now, COVID-19 seems to carry about the same short-term clot risk as other chest infections, a big change from the early years of the pandemic. Observational records from 12 US health systems with high vaccination rates; it cannot prove cause, and some comparison patients may have had undiagnosed COVID-19.
See the evidence
Retrospective study of US electronic health records (N3C) covering about 756,000 adults with COVID-19 and 679,000 with other respiratory infections, March 2020 to November 2024.
From the study: “Patients with COVID-19 had an increased risk of VTE (odds ratio [OR]: 1.45) and mortality (OR: 1.80) compared to the ARI cohort.”
Late Omicron: 1.0× odds
Soff SP et al. A comprehensive assessment of the impact of COVID variant and vaccination on venous thromboembolism and mortality. Research and practice in thrombosis and haemostasis. 2026.
From the study: “Contemporary (5/1/22 - 11/1/24) 277,278 / 297,464 1.01 (0.92-1.10)”
Late Omicron: 1.0× odds
Soff SP et al. A comprehensive assessment of the impact of COVID variant and vaccination on venous thromboembolism and mortality. Research and practice in thrombosis and haemostasis. 2026.
From the study: “However, risk was attenuated later in the pandemic, with similar risk between patients with COVID-19 and ARI in the Contemporary Omicron period (May 2022-Nov 2024)”
Late Omicron: 1.0× odds
Soff SP et al. A comprehensive assessment of the impact of COVID variant and vaccination on venous thromboembolism and mortality. Research and practice in thrombosis and haemostasis. 2026.
COVID-19 vaccination was linked to far fewer clots after infection.
78% lower clot riskVein clots within 30 days of infection, vaccinated vs unvaccinated (hazard ratio 0.22)
In health records from the UK, Spain and Estonia, vaccinated people had a 78% lower risk of a vein clot in the 30 days after a COVID-19 infection than unvaccinated people (hazard ratio 0.22), and a 47% lower risk of artery clots such as strokes and heart attacks (0.53). The benefit faded but lasted: 91 to 180 days after infection, vein-clot risk was still 47% lower (0.53).
This suggests vaccination lowers the clot danger that can follow COVID-19, and that part of the benefit lasts for months after an infection. Observational study of vaccine rollouts in three European countries; even after statistical corrections, vaccinated and unvaccinated people may differ in ways that skew results.
See the evidence
Staggered cohort study using health records of about 10 million vaccinated and 10 million unvaccinated people in the UK, Spain and Estonia during the vaccine rollout.
From the study: “Vaccination was associated with reduced risks of acute (30-day) and post-acute COVID-19 VTE, ATE and HF”
78% lower clot risk
Mercadé-Besora N et al. The role of COVID-19 vaccines in preventing post-COVID-19 thromboembolic and cardiovascular complications. Heart (British Cardiac Society). 2024.
From the study: “meta-analytic sHR of 0.22 (95% CI 0.17 to 0.29), 0.53 (0.44 to 0.63) and 0.45 (0.38 to 0.53), respectively, for 0-30 days after SARS-CoV-2 infection”
78% lower clot risk
Mercadé-Besora N et al. The role of COVID-19 vaccines in preventing post-COVID-19 thromboembolic and cardiovascular complications. Heart (British Cardiac Society). 2024.
From the study: “while in the 91-180 days sHR were 0.53 (0.40 to 0.70), 0.72 (0.58 to 0.88) and 0.61 (0.51 to 0.73), respectively.”
78% lower clot risk
Mercadé-Besora N et al. The role of COVID-19 vaccines in preventing post-COVID-19 thromboembolic and cardiovascular complications. Heart (British Cardiac Society). 2024.
Even past the first month, COVID-19 survivors had more vein clots.
9.9 more clots per 1,000Excess vein clots per 1,000 in the year after surviving COVID-19's first 30 days
US veterans who survived the first 30 days of COVID-19 had 2.39 times the risk (hazard ratio) of vein clots in the lungs, legs or surface veins over the next 12 months, compared with a same-period group without COVID-19: about 9.9 extra cases per 1,000 people. Stroke risk was 1.52 times higher, about 4.03 extra per 1,000. These risks appeared even in people not hospitalized for their infection.
Clot danger did not end when the infection did, even for people who recovered at home, so the months after COVID-19 matter too. Observational study of US Department of Veterans Affairs health records, so it shows links, not proof that COVID-19 caused the clots.
See the evidence
National cohort of about 154,000 US veterans with COVID-19 compared with millions of veterans without it, each followed for about a year.
From the study: “The risks and burdens of a composite of these thromboembolic disorders were 2.39 (2.27, 2.51) and 9.88 (9.05, 10.74).”
9.9 more clots per 1,000
Xie Y et al. Long-term cardiovascular outcomes of COVID-19. Nature medicine. 2022.
From the study: “People who survived the first 30 d of COVID-19 exhibited increased risk of stroke (hazard ratio (HR) = 1.52 (1.43, 1.62); burden 4.03 (3.32, 4.79) per 1,000 persons at 12 months”
9.9 more clots per 1,000
Xie Y et al. Long-term cardiovascular outcomes of COVID-19. Nature medicine. 2022.
New lasting high blood pressure followed COVID-19 more often than flu.
1 in 5 hospitalized20.6% of hospitalized COVID-19 patients had new, lasting high blood pressure at 6 months
Among patients at a New York City health system with no prior high blood pressure, 20.6% of those hospitalized with COVID-19 and 10.85% of those not hospitalized had new, persistent hypertension about 6 months later. Rates were higher than in influenza patients, and higher in older adults, men, Black patients and people with existing chronic illnesses.
Because so many people have had COVID-19, even this rate could mean many new cases of high blood pressure; the authors suggest screening at-risk patients afterward. Observational study within one New York City health system, so it cannot prove COVID-19 caused the high blood pressure.
See the evidence
Retrospective records study of about 45,000 COVID-19 patients (2020–2022) and 14,000 flu patients (2018–2022) without prior hypertension at a New York City academic health system.
From the study: “At 6-month follow-up, new-onset persistent hypertension was seen in 20.6% of hospitalized patients with COVID-19 and 10.85% of nonhospitalized patients with COVID-19.”
1 in 5 hospitalized
Zhang V et al. Incidence of New-Onset Hypertension Post-COVID-19: Comparison With Influenza. Hypertension (Dallas, Tex. : 1979). 2023.
Full-dose heparin helped moderately ill patients survive without life support.
About 1 in 25 helpedFrom a 4.0-point gain in surviving to discharge without life support, full vs usual dose
In a randomized trial of adults hospitalized with COVID-19 who were not critically ill, full-dose heparin (a blood thinner) instead of the usual lower preventive dose raised survival to discharge without intensive-care breathing or heart support by 4.0 percentage points, about 1 in 25 patients treated. Major bleeding occurred in 1.9% versus 0.9%.
The dose of a common blood thinner changed outcomes for hospital patients who were not yet critically ill, though the gain came with a small rise in serious bleeding. Open-label randomized trial (doctors and patients knew the dose given) that enrolled hospital patients from April 2020 to January 2021.
See the evidence
International randomized trial combining three platforms (ATTACC, ACTIV-4a, REMAP-CAP) with about 2,200 non-critically ill hospitalized COVID-19 patients, 2020–2021.
From the study: “The adjusted absolute between-group difference in survival until hospital discharge without organ support favoring therapeutic-dose anticoagulation was 4.0 percentage points”
About 1 in 25 helped
ATTACC Investigators et al. Therapeutic Anticoagulation with Heparin in Noncritically Ill Patients with Covid-19. The New England journal of medicine. 2021.
From the study: “Major bleeding occurred in 1.9% of the patients receiving therapeutic-dose anticoagulation and in 0.9% of those receiving thromboprophylaxis.”
About 1 in 25 helped
ATTACC Investigators et al. Therapeutic Anticoagulation with Heparin in Noncritically Ill Patients with Covid-19. The New England journal of medicine. 2021.
Women who had COVID-19 had stiffer arteries; men showed no difference.
Arteries ~5 years olderAuthors' rough estimate for women, at age 60 with normal blood pressure
Women who had COVID-19 had stiffer large arteries (pressure waves traveled 0.55 to 1.09 m/s faster) than women without COVID-19, across illness severities; men showed no difference. The authors estimate a 0.5 m/s rise equals roughly 5 years of extra vascular ageing for a 60-year-old with normal blood pressure. Among people who had COVID-19, stiffness held steady or improved by 12 months.
Stiffer arteries are a marker of blood-vessel ageing, so this hints COVID-19 may leave a mark on women's vessels, though the 12-month results suggest it can partly reverse. Observational study that first measured people about 6 months after infection, so stiffer arteries may have existed before COVID-19.
See the evidence
International prospective study at 34 centres in 16 countries measuring artery stiffness in about 2,400 adults with or without recent COVID-19.
From the study: “for a 60-year old person with normal BP a +0.5 m/s PWV roughly corresponds to +5 years of vascular ageing and +3% increased risk for CV events.”
Arteries ~5 years older
Bruno RM et al. Accelerated vascular ageing after COVID-19 infection: the CARTESIAN study. European heart journal. 2025.
From the study: “In sex-stratified analyses, PWV differences were significant in women [PWV (+0.55, +0.60, and +1.09 m/s for groups 2-4, P < .001 for all)], but not in men.”
Arteries ~5 years older
Bruno RM et al. Accelerated vascular ageing after COVID-19 infection: the CARTESIAN study. European heart journal. 2025.
A blood thinner after hospital discharge cut clots or cardiovascular deaths.
About 1 in 17 sparedFrom 3% vs 9% with clots or cardiovascular death by day 35, rivaroxaban vs none
In a randomized trial in Brazil of high-risk patients leaving the hospital after COVID-19, those given 35 days of the blood thinner rivaroxaban had clots or cardiovascular death in 3% of cases versus 9% with no blood thinner, so about 1 in 17 treated were spared. The count included clots found by routine scans. No major bleeding occurred in either group.
The weeks after leaving the hospital can still bring clots; this trial found that extending blood-thinner protection helped higher-risk patients without causing major bleeding. Small open-label trial of 320 patients in Brazil, funded by Bayer, with some clots detected only through routine scans.
See the evidence
Randomized trial at 14 Brazilian hospitals enrolling 320 high-risk patients discharged after COVID-19 hospitalization, October 2020 to June 2021.
From the study: “The primary efficacy outcome occurred in five (3%) of 159 patients assigned to rivaroxaban and 15 (9%) of 159 patients assigned to no anticoagulation”
About 1 in 17 spared
Ramacciotti E et al. Rivaroxaban versus no anticoagulation for post-discharge thromboprophylaxis after hospitalisation for COVID-19 (MICHELLE): an open-label, multicentre, randomised, controlled trial. Lancet (London, England). 2022.
From the study: “No major bleeding occurred in either study group.”
About 1 in 17 spared
Ramacciotti E et al. Rivaroxaban versus no anticoagulation for post-discharge thromboprophylaxis after hospitalisation for COVID-19 (MICHELLE): an open-label, multicentre, randomised, controlled trial. Lancet (London, England). 2022.
From the study: “In patients at high risk discharged after hospitalisation due to COVID-19, thromboprophylaxis with rivaroxaban 10 mg/day for 35 days improved clinical outcomes”
About 1 in 17 spared
Ramacciotti E et al. Rivaroxaban versus no anticoagulation for post-discharge thromboprophylaxis after hospitalisation for COVID-19 (MICHELLE): an open-label, multicentre, randomised, controlled trial. Lancet (London, England). 2022.
The combined death or vascular-hospitalization outcome was higher after Omicron COVID
Within 1 year, the combined outcome was 48.8% in Medicare beneficiaries aged ≥65 hospitalized with Omicron-era COVID-19 versus 33.4% in a historical 2017-2018 influenza-hospitalization cohort.
The outcome combines death from any cause or hospitalization for heart attack, ischemic stroke, transient ischemic attack, lung or deep-vein blood clots, heart failure or cardiac arrest. These historical groups were not a randomized comparison.
Study details & original results
Decker, Sérgio R R et al.. Long-term Cardiovascular Outcomes in US Medicare Beneficiaries After COVID-19 Hospitalization During the Omicron Era.. Circulation. Population health and outcomes. 2026.
Within 1 year, composite risk of all-cause death or hospitalization for myocardial infarction, ischemic stroke, transient ischemic attack, pulmonary embolism, deep vein thrombosis, heart failure, or cardiac arrest among Medicare beneficiaries aged ≥65 hospitalized with Omicron-era COVID-19 versus a historical 2017-2018 influenza hospitalization cohort.
48.8% vs 33.4%; risk difference 15.4% 95% CI: 15.1%-15.6%
Dates show when findings were added here, not when papers were published. Study populations and comparisons differ.
WHEN YOU WANT TO GO DEEPERSee all 1 findingsOriginal results, comparisons and study details.
1 of 1 source groupsFindings stay together with their study.
SOURCE 011 finding
Decker, Sérgio R R et al.. Long-term Cardiovascular Outcomes in US Medicare Beneficiaries After COVID-19 Hospitalization During the Omicron Era.. Circulation. Population health and outcomes. 2026.
Within 1 year, composite risk of all-cause death or hospitalization for myocardial infarction, ischemic stroke, transient ischemic attack, pulmonary embolism, deep vein thrombosis, heart failure, or cardiac arrest among Medicare beneficiaries aged ≥65 hospitalized with Omicron-era COVID-19 versus a historical 2017-2018 influenza hospitalization cohort.
Added
48.8% vs 33.4%; risk difference 15.4%95% CI: 15.1%-15.6%Source [1]
Browse the 10 original sourcesThe complete bibliography behind this monitor.
[1]
Decker, Sérgio R R et al.. Long-term Cardiovascular Outcomes in US Medicare Beneficiaries After COVID-19 Hospitalization During the Omicron Era.. Circulation. Population health and outcomes. 2026.
Fernández-Sanlés, Alba et al.. Multi-organ structural and functional deficits in association with long COVID: a population-based case-control study.. EClinicalMedicine. 2026.
Knight R et al. Association of COVID-19 With Major Arterial and Venous Thrombotic Diseases: A Population-Wide Cohort Study of 48 Million Adults in England and Wales. Circulation. 2022.
Soff SP et al. A comprehensive assessment of the impact of COVID variant and vaccination on venous thromboembolism and mortality. Research and practice in thrombosis and haemostasis. 2026.
Mercadé-Besora N et al. The role of COVID-19 vaccines in preventing post-COVID-19 thromboembolic and cardiovascular complications. Heart (British Cardiac Society). 2024.
ATTACC Investigators et al. Therapeutic Anticoagulation with Heparin in Noncritically Ill Patients with Covid-19. The New England journal of medicine. 2021.
Ramacciotti E et al. Rivaroxaban versus no anticoagulation for post-discharge thromboprophylaxis after hospitalisation for COVID-19 (MICHELLE): an open-label, multicentre, randomised, controlled trial. Lancet (London, England). 2022.
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