A team of researchers from the University of New South Wales (UNSW) and St Vincent's hospital Sydney have found a clear biological marker in patients experiencing long Covid.
The study, published in the Nature Immunology journal on Friday, used data collected from unvaccinated patients at St Vincent's hospital who were infected with the Alpha variant during Australia's first wave of the pandemic in early 2020, Xinhua news agency reported.
Chansavath Phetsouphanh, the Senior Research Associate at UNSW's Kirby Institute and co-lead author on the paper, said this study describes the long-term impact of Covid-19 on the immune system through analysis in a laboratory setting.
"We found that there is a significant and sustained inflammation that indicates prolonged activation of the immune system response detectable for at least eight months following initial infection," Phetsouphanh added.
Of the 62 Covid patients involved in the study, 30 per cent showed some symptoms of long Covid.
They found that patients that presented with long Covid held biomarkers of infection that disappeared in patients who had fully recovered from the disease.
"These are biological characteristics which can help us define a medical condition in an accurate and reproducible way," said Phetsouphanh.
Interestingly, the study found that the severity of one's experience with Covid-19 showed no link to developing the long-lasting symptoms seen in long Covid.
Supporting this finding, one participant in the study Doris Gal gave a first-hand account of her experience of long Covid.
"My initial infection was quite mild, however, my long Covid symptoms are significant. I've lost the ability to comprehend the way I did before having Covid," said Gal.
Proving the biological basis for long Covid will not only open up ways to treat and monitor the condition, but it also, for patients like Gal, confirmed a biological basis of the ongoing impacts of the disease.
The researchers said that new studies would need to be conducted to see if the impacts of long Covid are milder or rarer in those who have been vaccinated or with different variants, such as the now dominant Omicron variant.
"We will continue our analysis in response to the Omicron wave. In the meantime, with so many unknowns with both Covid and long Covid, we should do everything we can to reduce transmission," said Kirby Institute Director, Anthony Kelleher.