BLOOD SCIENCES
their condition within a few days or weeks after the onset of symptoms, achieving a complete recovery within a 12-week period. However, for certain people the symptoms may persist for a longer duration. According to the UK National Health Service (NHS) the most common symptoms of long COVID are extreme tiredness (fatigue), muscle aches, joint pain, shortness of breath, heart palpitations, dizziness, and problems with memory and concentration, often referred to as ‘brain fog’.
As per the UK Office for National Statistics reports, approximately two million individuals residing in private households in the UK, representing 3.1% of the population, reported experiencing long COVID.7
Fatigue remained the
predominant symptom, with 60% indicating this issue. Additionally, it was reported that 37% of the participants faced challenges related to memory and concentration, while 48% of patients experienced shortness of breath. Also, 34% reported joint pain and 42% indicated experiencing muscle discomfort.8 Following recovery from the initial viral infection, it has been found that around 7% of cases continue to have some of the same structural spike proteins (spike glycoprotein) found in active COVID-19 patients, which continues to circulate within the blood stream.9 Hypercoagulability, a condition
where the blood is more prone to clots than normal has been reported, while fibrinolysis – which is a normal body process of dissolving blood clots by breaking down the fibrin network – has also been found as a consequence. Both hypercoagulability and fibrinolysis are well recognised features amongst some COVID-19 patients.10 During the disease process fibrinogen will have been deposited in the lungs and brain tissue and this correlates with disease activity. The study by Ryu et al., (2024) state that fibrinogen can be used as biomarker and show that fibrin binds to the spike protein forming proinflammatory blood clots which promote systemic thromboinflammation and neuroinflammation.10
These inflammatory mediators that can activate platelets and coagulation factors. Activated platelets release pro-inflammatory molecules, further amplifying the inflammatory response. The author states: “Fibrin promotes
neuroinflammation and neuronal loss after infection, as well as innate immune activation in the brain and lungs independently of active
Long COVID symptoms Cough
Shortness of breath Loss of smell and taste Joint pain Brain fog Fatigue
Heart palpitations Depression
Table 1. Long COVID symptoms.6
infection.” Concluding that fibrin drives inflammation and neuropathology in the patients.
As these COVID spikes flow
throughout the circulation, they appear to bind with fibrinogen and partially activate it which is converted into fibrin clot creating a three-dimensional net. The fibrinogen activation initiates a further activation of platelets, which aggregate at the site activation, forming a platelet plug which becomes trapped in the net, and promotes the classical coagulation reaction resulting in micro clots.
Epidemiology and risk factors for long COVID Epidemiological research on long COVID presents challenges in interpretation and synthesis due to significant variations in sampling frameworks, inclusion criteria, demographic characteristics of participants, diagnostic standards, and research methodologies.
Despite the publication of thousands of academic articles, including 170 systematic reviews, a significant number of clinicians still lack clarity on how to assess, diagnose and treat patients with long COVID, the post-COVID-19 condition.
A significant number of individuals (but not all) suffering from long COVID possess pre-existing health conditions such as asthma, allergies, attention deficit hyperactivity disorder, musculoskeletal pain, diabetes, mental-health issues, insomnia, headaches, chronic fatigue, and frailty, which may worsen the effects of long COVID and vice versa. Table 2 summarises the risk factors for long COVID.
Long COVID study In a recent paper by Greenhalgh et al., (2024) it was indicated that the prevalence of long COVID has been assessed globally through various studies, with estimates ranging from 50% to 85% among hospitalised unvaccinated individuals, 10% to 35% among non- hospitalised unvaccinated individuals, and 8% to 12% among vaccinated individuals.12-17 A BBC health report in 2024 discussed the condition in an article about the largest long COVID study which was led by Imperial College London.18
The
study involved following up to 657 hospitalised patients who had suffered severe COVID-19 illness. It was reported that 35% individuals in the group had fully recuperated. After six months, 65% individuals presented with at least one symptom of long COVID.19
The study also found that the long COVID group consisted of approximately two third females and that if the symptoms were still present after six months they were highly likely to be present one or two years later. However, it has been noted that the number of new cases of long COVID is reducing from the original figure, probably reflecting the success of the vaccination programme; but the fact that the dominant variant was Omicron, but is now Stratus rather than the original strain, may also be a contributing factor.20 The research findings indicated that individuals suffering from long COVID displayed signs of ongoing inflammatory proteins in their blood. The investigators noted that the detection of these inflammatory protein substances in the bloodstream typically indicates the immune system’s reaction to an infection. This was unusual, when taking into account the considerable duration that had elapsed since the onset of the initial infection.
Data showed that prolonged symptoms do not appear to be directly correlated with the severity of the initial infection. Interestingly a cohort of those who initially had mild symptoms also reported being affected by long COVID. Lead researcher Professor Peter Openshaw stated that this study offers
Approximately two million UK individuals reported experiencing long COVID. Fatigue remained the predominant symptom, with 60% indicating this issue
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