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Since the beginning of the year when Omicron took hold in the U.S., physicians across the country have reported seeing fewer instances of blood clotting linked to COVID-19.

However, recent social media postings from members of the medical community in the U.K. -- which has served as a harbinger for what's to come in the U.S. throughout the pandemic -- have raised the possibility of a reversal of this trend.

Last week, Graham Lloyd-Jones, MBBS, MRCP, a radiologist with the Salisbury NHS Foundation Trust in the U.K., , sparking an extended thread from other healthcare professionals: "To all #radiologists. Have you seen the typical #COVID pulmonary vasculopathy on CXR/CT in the last week? We've not seen this since omicron became dominant Feb '22. I'm concerned we have a new variant which causes the same clotting in the lungs as delta/pre-delta."

Responses to the post were mixed, with some saying that they had once again seen serious lung involvement with recent COVID cases and others saying they hadn't yet observed what Lloyd-Jones had alluded to. Even more responded with general concern and questions.

In an , the U.K. Health Security Agency detailed that there were indeed a number of new variants that had begun to circulate in recent weeks.

"The development of these additional lineages has been rapid," the report read. "They have varying Omicron backbones but some convergent receptor-binding domain (RBD) mutations ... which are likely to produce a degree of escape from current immunity in the U.K."

Specifically, the report noted BQ.X, BA.2.75.2, and BF.7 as the most concerning variants for the U.K. in terms of both growth and neutralization data. However, the report also mentioned BQ.1.1, which has been reported in about 20 countries and in dozens of U.K. samples, and several other variants in other parts of the world, as part of its horizon scanning.

Even with new variants emerging, though, it appears that many radiologists in the U.K. and the U.S. have not yet observed any recent uptick in COVID-related blood clots.

A spokesperson for the Royal College of Radiologists in the U.K. declined to comment on behalf of its officers.

For the U.S., Ella Kazerooni, MD, chair of the American College of Radiology's National Radiology Data Registries and Lung Cancer Screening Registry, said in a statement provided to 麻豆传媒 that she and her colleagues have not necessarily seen the trend.

"We saw a decrease in pulmonary embolism/deep vein thrombosis clots as Omicron became the dominant strain in the U.S. last winter with the BA.1, BA.2, BA.4 and BA.5 variants, and are not yet seeing a fall/winter case spike here at this time," said Kazerooni, a professor of radiology and internal medicine at the University of Michigan Medical Group in Ann Arbor.

At the same time, she added the following: "Omicron BQ.1.1 is a relatively new sub-variant that was discovered a few weeks ago and is on the rise in Europe. It was also detected in Canada last month, but we are not seeing it here yet. The U.S. generally experience new variants later than European countries."

"The new strain is a descendant of the Omicron BA.5 sub-variant that has been the dominant strain in the U.S. and Canada since last winter," she pointed out. "What the future holds as variants change is something we continue to follow closely."

Jonathan Paul, MD, director of the Pulmonary Embolism Response Team at the University of Chicago Medicine, also told 麻豆传媒 that, earlier in the pandemic, "the blood clots in the legs and the lungs were a bigger problem than they are now."

"As the different variants progressed on ... the incidence of blood clots has gone down," Paul said.

There may likely be a number of factors contributing to that, he said, including recently circulating variants being less likely to cause severe inflammation -- which is one of the risk factors for blood clots -- and more people becoming vaccinated.

However, as with everything related to the coronavirus, it's a "moving target," he acknowledged. "We're learning more and more every week."

Thrombosis remains one of the major complicating factors of COVID, Paul said, whether that be a large clot traveling from the legs up into the lungs or a collection of smaller clots there. In fact, the obstruction of tiny vessels in the lungs is one hypothesis for what may cause long COVID in some patients, he said.

Blood thinners are still being used in hospitalized COVID patients, Paul added, and there are some patients -- both those who have been hospitalized and those who have experienced milder infections -- presenting with blood clots even months later.

"Could a future variant be associated with higher risk of blood clots?" Paul said. "Sure, it could."

But what may be more important than looking ahead is simply calling attention to symptoms that may arise now.

"People think about losing taste, shortness of breath ... but swelling in the extremities or having these chronic fatigue symptoms could be related to blood clots," Paul said. "As a medical community [we need to] do a better job to raise awareness of the acute and long-term complications that could include blood clots."

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