Blood samples from people with long Covid who are still suffering with symptoms after 12 months show signs of autoimmune disease, a new study has found.

Autoimmune diseases, such as rheumatoid arthritis and lupus, occur when the immune system mistakenly attacks healthy parts of the body instead of defending the body against disease.

Lead researcher, Dr Manali Mukherjee of McMaster University in Ontario, Canada, began to wonder about the role of the immune system in long Covid after she experienced symptoms firsthand.

“Although long Covid is now recognised by bodies like the World Health Organization, we still know very little about why it develops or how we can help patients,” she noted.

She and her colleagues recruited 106 people who had been diagnosed with Covid-19 between August 2020 and September 2021 and were under the care of three hospitals in Canada. They also included a group of 22 healthy volunteers and a group of 34 people who had experienced a non-Covid respiratory infection as a comparison.

On three occasions – three, six and 12 months after they recovered from infection – patients were asked if they were suffering any shortness of breath, coughing or fatigue, all of which are typical symptoms of long Covid.

Most patients were still taking part in the study after six months (98 out of 106) while only 57 came back after 12 months. The researchers suggested that this may be due to patients recovering.

The participants provided blood samples and these were tested for particular antibodies. Antibodies are normally produced by the immune system to stick to potentially harmful bacteria or viruses, marking them out for attack by other parts of the immune system. In this case, the researchers looked for antibodies that target healthy cells and tissues in the body and that are known to contribute to autoimmune diseases.

The study found that almost 80% of the Covid-19 patients had two or more of these antibodies in their blood three months and six months after the infection. This fell to 41% after a year. Most of the healthy volunteers had no sign of these antibodies in their blood and in those who had experienced a non-COVID respiratory infection, levels of these antibodies were comparatively low.

Researchers also found that two specific ‘autoantibodies’ (called U1snRNP and SSb-La autoantibodies), along with cytokines that cause inflammation, persisted in around 30% of Covid patients a year after infection. This tended to be among those patients who were also still suffering with fatigue and shortness of breath.

“For the majority of the patients in our study, even if they had autoantibodies soon after their infection, this resolved after 12 months. However, in some patients, autoantibodies persist, and these patients are more likely to continue suffering with symptoms and to need medical help. These results point towards the need to test for signs of autoimmune disease in patients with symptoms of long Covid that last for a year or more,” Dr Mukherjee said.

According to co-lead researcher, Prof Chris Carlsten of the University of British Columbia in Vancouver, these findings on autoantibodies support the findings of other researchers “and provide strong plausibility for the presentation of long Covid as a systemic disease”.

The researchers are now planning to study long Covid patients over a period of two years to see how the levels of autoantibodies change in the longer term.

The study is published in the European Respiratory Journal and according to Dr Eva Polverino from Vall d'Hebron University Hospital in Barcelona, Spain, and head of the European Respiratory Society’s Respiratory Infections Assembly, despite millions of people worldwide suffering with long Covid, there is a lack of evidence on why some people develop the condition and how patients can be helped.

“We know that certain infections can, in some cases, trigger longer-term autoimmune diseases such as rheumatoid arthritis. This study adds to growing evidence that similar processes may be involved in long Covid. Further work in this area could increase our understanding of long Covid and how best to diagnose and treat the condition,” she commented.