What is long Covid?
Generally, when an individual has a positive test for Covid-19 they start to feel better within a few days or weeks and most people will make a full recovery within 12 weeks. However, for some people, these symptoms can last longer, even with a negative test. This is known as long Covid.
What are the symptoms of long Covid?
There are several symptoms associated with long Covid including;
Extreme tiredness (fatigue)
Shortness of breath
Chest pain or tightness
Problems with memory and concentration ("brain fog")
Difficulty sleeping (insomnia)
Pins and needles
Depression and anxiety
Feeling sick, diarrhoea, stomach aches, loss of appetite
A high temperature, cough, headaches, sore throat, changes to sense of smell or taste
Why do some people suffer from long Covid?
Research has suggested that those who are older and show a wider range of symptoms when initially infected are more likely to develop long Covid. Research at King’s College London also suggests that females, being overweight and having asthma could also increase your risk.
Covid and the gut microbiome
Our gut and lungs are constantly talking to each other. This is known as the gut-lung axis and recent evidence suggests it plays an important role in Covid-19 and may influence how severely you suffer.
Like our gut, our lungs have bacteria communities that interact with viral infections and affect how they progress and how severely you may suffer. Research suggests dysbiosis may play an important role in the development of common respiratory diseases and infection via the gut-lung axis.
A group of researchers investigated whether differences in our gut microbiome can influence Covid outcomes. 100 patients were recruited who had tested positive for Covid-19 (confirmed by positive SARS-Cov-2 RT-qPCR). The researchers took blood and stool samples from each participant and measured their response to the infection over 30 days.
The severity of Covid-19 was classified as mild in the absence of x-ray evidence of pneumonia; moderate if pneumonia with fever and respiratory tract symptoms were detected; severe if patients found it very difficult to breathe normally; and critical if they needed mechanical ventilation or experienced organ failure requiring intensive care.
The results showed that the gut microbiota composition of patients with Covid-19 during hospitalisation is correlated with plasma concentrations of several cytokines, chemokines and inflammation markers. Lower numbers of Faecalibacterium prausnitzii and Bifidobacterium bifidum were associated with infection severity after taking account of antibiotic use and patient age.
This suggests that the gut microbiota could play a role in modulating host immune response and potentially influence disease severity and outcomes.
Additionally, there was a subset of patients who once tested negative for Covid-19 experienced persistent symptoms such as fatigue, dyspnoea (difficult or laboured breathing) and joint pains, some over 80 days after the initial onset of symptoms. This suggests that the gut microbiome could contribute to symptoms experienced in long Covid.
Unfortunately, this was a short-term study and further studies need to be carried out with a longer follow up period to fully explore the link between the gut microbiome and long Covid. It is also important to note that this is an observational study, so it cannot indicate whether variation in the gut microbiome is determining COVID-19 severity or whether the virus itself has caused this variation.
However, the initial research suggests there may be a link between Covid-19 and the gut microbiome and therefore, targeting the microbiome (i.e., through probiotics) might be a potential treatment method for both initial treatment of Covid and to help prevent long Covid.
nhs.uk. 2021. Long-term effects of coronavirus (long COVID). [online] Available at: [Accessed 30 March 2021].
Bmj.com. 2021. Make-up of gut microbiome may influence COVID-19 severity and immune response | BMJ. [online] Available at: [Accessed 30 March 2021].
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