A possible link between blood clots and ongoing symptoms of Covid is under scrutiny by researchers in the UK.
While Covid can cause a period of acute illness, it can also lead to longer-term problems. Research has suggested fewer than a third of patients who have ongoing Covid symptoms after being hospitalised with the disease feel fully recovered a year later.
Now researchers are due to begin a number of trials to explore 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 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 suggested that people with long Covid have microclots in their blood, while studies in the UK suggested almost a third of long Covid patients have clotting abnormalities.
But he said it was not clear if the findings were generalisable, and while there had been calls on social media for anticoagulants to be made available on the basis of such findings, further research was needed, not least as blood thinners can lead to an increased risk of bleeds.
The point was echoed by Prof Betty Raman, of the University of Oxford, who 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 indeed a cause of ongoing Covid symptoms.
“There needs to be more dedicated studies looking at the efficacy of anticoagulants [for long Covid], just like how we did with [treatments for] the acute unwell patients,” Raman said.
The Stimulate-ICP trial, which is due to start recruiting within 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 say whether that improves the fatigue and other outcomes of people with long Covid,” said Banerjee.
While the trial focuses on people who had Covid in the community, another study, called Heal-Covid, involves people who were hospitalised with the disease, aiming to identify treatments that may help to prevent or reduce ongoing symptoms.
“Heal-Covid is not a study treating people with long Covid, we are aiming to prevent things getting to that point,” said Prof Charlotte Summers, of the University of Cambridge, who is chief investigator on the work.
The team 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 increased number of large blood clots occurring in the post-hospital phase of the illness rather than microclots,” Summers said.
The post-hospitalisation Covid-19 study – or Phos-Covid – which has offered key insights into long Covid, is also probing the issue of clotting.
Chris Brightling, a professor of respiratory medicine at the University of Leicester and chief investigator on the study, said one area the team was looking at was whether people with ongoing symptoms after hospitalisation have chronic thromboembolic pulmonary hypertension. Should this be found, he said, it would be strong evidence that microclots are a substantial problem.
“Whereas if we don’t see that, that doesn’t exclude the possibility that, obviously – certain individuals get clots – but it would make it less likely that it’s intrinsically a major problem,” he said.
Banerjee said that while it was understandable some patients with ongoing symptoms of Covid may be frustrated that certain therapies were not yet available, rigorous studies were essential. “We need to make sure that we don’t [lower] the bar for safety,” he said.