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Gut bacteria affects how immune system responds to Covid, studies say

Bacteria in a person’s gut could determine how seriously they’re affected by symptoms of Covid, two new studies in Asia have found. 

Research carried out by scientists at the University of Hong Kong found that some people diagnosed with the virus had a ‘significantly altered’ microbiome after recovery, while the results of a recent study in South Korea suggests that people lacking in a healthy microbiome could fare worse when fighting the illness.

The bacteria composition found in the body’s microbiome is different for every individual – with health, diet and environment all factors in gut health, which can play a substantial role in helping the immune system’s defences.

Researchers in Hong Kong tested blood and stool samples from 100 patients who contracted the Covid virus in the four months from February 2020, and then tested them again 30 days after recovery.

The findings showed that those who had a gut microbiome that didn’t function well suffered with symptoms for longer than those with a healthy microbiome.

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Published in the health journal Gut, researchers from the University of Hong Kong said: “In light of reports that a subset of recovered patients with COVID-19 experience persistent symptoms, such as fatigue, dyspnoea [breathlessness] and joint pains, some over 80 days after initial onset of symptoms, we posit that the dysbiotic gut microbiome could contribute to immune-related health problems post-COVID-19.”  

The study showed that the virus transformed the microbiome for at least 30 days after infection, with some patients presenting with elevated levels of bacteria including Ruminococcus gnavus, Ruminococcus torques and Bacteroides dorei, while good bacteria known to help the immune system – including Faecalibacterium prausnitzii and Bifidobacterium bifidum – were found to be depleted in patients who’d had the virus.

Higher levels of cytokines, tiny molecules which are part of the immune system, were also found to be negatively affected by the virus.

The paper concludes that the gut may be involved in the ‘magnitude of Covid-19 severity possibly via modulating host immune responses’.

Meanwhile, researchers at Korea University’s Laboratory for Human-Microbial Interactions studied data from a variety of research programmes examining poor gut health in relation to Covid infections.

Lead scientist Dr Heenam Stanley Kim said there appears to be significant evidence to support claims that the gut can play an integral role in how the the immune system responds to the virus, with poor gut health leaving patients more vulnerable to its symptoms.

Dr Kim said: “There seems to be a clear connection between the altered gut microbiome and severe COVID-19”.

Korea University's Laboratory for Human-Microbial Interactions, University of Hong Kong