AN OVER-ACTIVE immune response to Covid-19 could be part of the reasons why some people experience long Covid symptoms such as fatigue months after their infection, according to a new study.

Scientists at a research centre in University College Cork (UCC) examined 24 patients who had been hospitalised with Covid-19 during the first pandemic wave last spring.

The patients attended post-Covid infection clinics and the most common symptoms reported in the months after infection were fatigue and/or difficult breathing.

While in hospital, the severity of their illnesses ranged from mild to critical.

From analysing this small number of cases, researchers found that people with long Covid symptoms showed “significant and demonstrable disturbances” in their immune signalling networks for up to nine months after they were discharged from hospital. 

The researchers said this data suggests there are long-term impacts to the immune system after infection “at least in those that had acute symptoms severe enough to require hospitalisation”. 

Your immune system protects against viruses and diseases. When your immune system encounters viruses like the SARS-CoV-2 coronavirus for the first time, it can’t work fast enough to fight infection and illnesses can occur. 

The researchers found that people whose immune systems had an over-active response to Covid could get long Covid symptoms down the line. 

They said this kind of study is important to understand how long Covid affects the “daily functioning and the quality of life” of patients. 

Professor Liam O’Mahony, a professor of immunology at APC Microbiome Ireland, a research centre based in UCC, said the research results show there can be “significant determinantal long-term effects” from Covid-19 that can impact daily life “even months after the initial infection has been cleared”. 

“However, the reasons why some people develop these long-term symptoms are not clear,” O’Mahony said in a statement.

“One potential reason is that the immune system may remain in a semi-activated state for a long time following infection.”

Professor O’Mahony’s researchers joined up with Dr Corinna Sadlier, an infectious disease consultant at Cork University Hospital to conduct this research.

Dr Sadlier said patients can experience “debilitating” long Covid symptoms that can “significantly” impact their quality of life.

“Translational research such as this will be critical in understanding the mechanism underlying these ongoing symptoms from both a diagnostic and therapeutic perspective so we can optimally manage these patients in the future,” she added.

A statement on the study said: “The relatively low number of patients included in this study to date does not allow for researchers to perform subgroup analysis, but the findings may be of clinical value if replicated in future studies.

The median age of the patients examined was 53.5 years.

A UK study published in January found that the likelihood of severe and long Covid may be established early on after infection.

It found that people who required admission to hospital have impaired immune responses and systemic inflammation – chronic inflammation that may affect several organs – from the time of symptom onset.

Scientists involved in the study said persistent abnormalities in immune cells and a change in the body’s inflammatory response may contribute to long Covid.

A UK immunologist said in February that cases of long Covid could be as high as 10-20% of people with the disease.