Blood clots linked to long Covid symptoms

Researchers in the UK have examined the link between blood clots and ongoing symptoms of Covid.

Covid can cause a period of acute illness, but it can also lead to longer-term problems. Despite being hospitalised with the disease, fewer than a third of patients with ongoing Covid symptoms feel fully recovered a year later, according to research.

Researchers are about to start a number of trials to examine whether blood thinners may help those who have had the disease.

Prof Ami Banerjee, of University College London, who is leading a study called Stimulate-ICP, said that it was known that a Covid infection increases the risk of blood clots, and that people who have had the disease have a greater risk of related conditions, including stroke, heart attacks and deep vein thrombosis.

In addition, Banerjee said research from scientists in South Africa had shown that people with long Covid have microclots in their blood, while studies in the UK suggested that almost a third of long Covid patients have clotting abnormalities.

He said it was not clear if the findings were generalisable, and there had been calls on social media for anticoagulants to be made available on the basis of such findings, but further research was needed, not least because blood thinners can lead to an increased risk of bleeding.

The professor Betty Raman, of the University of Oxford, cautioned that studies into microclots and long Covid had not yet been carried out on a large scale. Microclots were difficult to screen for, and it was not yet clear whether clotting abnormalities are a cause of ongoing Covid symptoms.

There need to be more dedicated studies looking at the efficacy of anticoagulants for long Covid, like we did with treatments for acute unwell patients, Raman said.

The Stimulate-ICP trial, which will start recruiting within a few days, will split 4,500 people with long Covid into four groups in which participants are allocated usual care, antihistamines, an anti-inflammatory or an anti-clotting drug for three months. That will allow us to determine whether that improves the fatigue and other outcomes of people with long Covid, said Banerjee.

The trial focuses on people who had Covid in the community, while another study, called Heal-Covid, involves people who have been hospitalised with the disease, aiming to identify treatments that may help to prevent or reduce ongoing symptoms.

Heal-Covid is not a study for people with long Covid, but we are aiming to prevent things from getting to that point, said Professor Charlotte Summers, of the University of Cambridge, who is chief investigator on the work.

The trial has recruited 1,118 participants with one arm of the trial involving participants receiving blood thinners. The trial included anticoagulants as there was thought to be an increase in the number of large blood clots occurring in the post-hospital phase of the illness rather than microclots, Summers said.

The post-hospitalization Covid 19 study or Phos-Covid, which has given key insights into long Covid, is also probing the issue of clotting.

Chris Brightling, professor of respiratory medicine at the University of Leicester and chief investigator on the study, said one area that the team looked at was whether people with ongoing symptoms after hospitalisation have chronic thromboembolic pulmonary hypertension. If this is found, it would be strong evidence that microclots are a serious problem, he said.

He said that if we don't see that, that doesn't exclude the possibility that certain individuals get clots, but it would make it less likely that it is a major problem.

Banerjee said rigorous studies were essential, because some patients with ongoing symptoms of Covid may be frustrated that certain therapies are not yet available. He said that we need to make sure that we don't lower the bar for safety.