It isn’t the jab you need to fear – even mild Covid can trigger deadly clots: With reports of people shunning the AstraZeneca vaccine, we look at the (very rare) risk
Three days after testing positive, Robin suddenly felt so weak while out in the garden he couldn’t lift his arms to use the hedge clippers
Robin McNelis’s Covid-19 symptoms were so mild he didn’t know he’d had the disease.
It was only when a routine test at the hospital where he works as a respiratory physiotherapist came back positive that he found out his headache and fatigue were caused by the virus.
‘I was surprised to be told I had tested positive and should stay off work,’ says Robin, 47, who lives in Stapleford Abbotts, Essex, with his wife Nikki, 45, a project manager, and daughter Maya, 13.
‘I’d had no temperature or dry cough, but had lost my senses of taste and smell. I thought I’d got off lightly.’
But three days after testing positive, Robin suddenly felt so weak while out in the garden he couldn’t lift his arms to use the hedge clippers.
‘I lost my balance and felt dizzy, falling to the ground, twice,’ he says. ‘I sat down on a garden bench and immediately fell asleep for about five minutes. Then I got up and went back into the house, but struggled to walk up the stairs.’
None of this made sense. As a seasoned marathon runner, Robin was exceptionally fit. But the problems continued. He had to keep stopping when walking uphill, and felt a tightness across his chest and back when exercising.
After three weeks off, he returned to work at the private Wellington Hospital in London. However, he was still struggling with fatigue, chest pain and weak legs, so he was referred for a telephone assessment with a GP.
‘The GP asked me to measure my blood oxygen levels after climbing the stairs,’ says Robin, who used a pulse oximeter, which measures blood oxygen levels by sending light through the tiny blood vessels in the fingertip.
‘My levels were good but, two hours later, I was still short of breath,’ he recalls.
A respiratory consultant sent Robin for a lung scan, which revealed that a small blood clot was causing the symptoms. Robin was told that the virus had made his blood ‘sticky’, encouraging blood cells to clump together to form a clot, which can be fatal if it blocks blood flow to the lungs.
Smaller clots, as in Robin’s case, can cause breathlessness as well as chest pain. ‘They weren’t sure if the clot had formed in the lung, or whether it was a clot that had developed in the deep veins of the legs or pelvis, that had broken off and travelled to the lungs,’ says Robin.
As a seasoned marathon runner, Robin was exceptionally fit. But the problems continued. He had to keep stopping when walking uphill, and felt a tightness across his chest and back when exercising
He was put on blood thinners to disperse the clot and prevent more forming. But he was fortunate that the outcome wasn’t far worse.
Last week, concerns about the AstraZeneca vaccine triggering fatal blood clots in a very small number of patients halted several countries’ roll-out of the jab.
The World Health Organisation, British and European regulators however insist that the jab is not linked to a raised risk of clots.
And yet, sticky blood, which can lead to blood clots, is a major problem for Covid patients, mostly those who have been hospitalised.
Between 30 and 70 per cent of Covid patients treated in intensive care develop a clot, according to a French study published last year in the journal Thrombosis and Haemostasis, but a clot can also form in others who, like Robin, have had a milder infection.
The problem is linked to the body’s extreme inflammatory response to the virus, which triggers the production of chemicals that instruct the liver to make more clotting proteins.
Some reports suggest that small blood clots form in Covid patients’ lungs as a result of inflammation switching on clotting locally.
Doctors don’t know how long the blood remains sticky in these patients, but believe it is stickiest at the height of the infection.
Last week, concerns about the AstraZeneca vaccine triggering fatal blood clots in a very small number of patients halted several countries’ roll-out of the jab. The World Health Organisation, British and European regulators however insist that the jab is not linked to a raised risk of clots
This is worrying because it not only raises the clot risk, but also the chances of stroke and heart attacks, according to Dr George Amin-Youssef, a consultant cardiologist at the Wellington Hospital and King’s College Hospital in London, who treated Robin.
To prevent clots, all patients admitted to hospital with Covid are now given blood thinners. Professor Beverley Hunt, medical director of the charity Thrombosis UK, says Covid patients have the stickiest blood she has ever encountered, with up to seven times the normal amount of the clotting protein fibrinogen.
‘Normally fibrinogen levels are between 2g and 4g per litre of blood, but Covid patients have levels of 8g and, extraordinarily, 14g in some cases, which I’ve never seen before,’ says Professor Hunt.
Sticky blood is a particular problem in patients with viral Covid pneumonia, she says.
‘Usually these patients are hospitalised because they are short of breath, and they will be given blood thinners,’ says Professor Hunt.
‘However, I am aware of other patients who were not hospitalised with a milder form of Covid pneumonia who also have sticky blood and are experiencing clot symptoms.’
This is borne out by Dr Amin-Youssef’s experience. ‘Most cases of sticky blood-related complications are in people who are treated in intensive care, but we are also seeing it in people who are not hospitalised, like Robin.’
‘Significant numbers’ of Covid patients who don’t require hospital treatment are developing clots, adds Dr James Hull, a consultant respiratory physician at the Royal Brompton Hospital and the private HCA Institute of Sport and Exercise Health, both in London.
‘You don’t have to have been hospitalised with Covid to get a pulmonary embolism,’ he says. ‘We’ve seen people with unexplained breathlessness following relatively mild symptoms of Covid, where the underlying cause is later discovered to be a clot.’
A clot can be diagnosed by a GP using blood tests to look for raised levels of D-dimer, a protein that’s a marker for clots.
If levels are raised, further tests including chest X-rays, an ECG and blood oxygen measurement may be needed.
Robin, who was also later diagnosed with pericarditis — inflammation of the lining of the sac protecting the heart — due to Covid, stayed on blood thinners for eight months until a scan in November showed that these had dispersed the clot.
‘Luckily, my clot was small and stable and didn’t block the pulmonary artery, otherwise it could have killed me,’ he says. ‘But it was a huge shock as I hadn’t been that ill with Covid, or gone into hospital. Don’t make the mistake of thinking you can’t have a clot because you weren’t “that ill”.’
He had a Covid vaccine — the Pfizer jab — in January. ‘Having suffered the effects of Covid, including blood clots, it wasn’t a hard decision to make,’ he says.
‘One year on from Covid, I’m still only working three days a week. I haven’t begun running again as I have post-Covid chronic fatigue, and won’t be doing a marathon any time soon’
n thrombosis uk.org
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