Long-term biochemical impacts from Covid-19 — even among mild cases — have been discovered in more than half those who get the virus.
A small study of people who got mild cases of Covid-19 in Australia has found some had "blood biochemical abnormalities" and more than half experienced symptoms six months after being infected.
Scientists working at the Australian National Phenome Centre (ANPC) at Murdoch University in Perth, Western Australia, investigated the blood chemistry of 27 patients who had mild forms of the disease.
"What we discovered is a majority of non-hospitalised Covid-19 patients are not back to normal health or normal biochemistry three months on, with one or more symptoms persisting in 57 per cent of those patients up to six months following the acute phase," ANPC director Professor Jeremy Nicholson said.
Symptoms could include chronic fatigue, muscle and joint pain and loss of sense of smell.
Importantly, many patients also had metabolic abnormalities that researchers believe could change their risks for other illnesses like heart disease.
"This is a major public health concern and warrants further investigation at the national and international level," Prof Nicholson said.
It comes after early results of another study showed about two in three Australians had ongoing health issues after being critically ill with Covid-19.
Prof Nicholson said more than 160 million people worldwide had suffered from a less severe form of Covid-19.
"We are undertaking follow-up studies to assess recovery and what we've found is cause for concern," he said.
"This is an immensely dangerous disease that is not only costing lives today, but as we're discovering now, may have serious health consequences for some patients long into the future, even in relatively mild original cases."
However, Nicholson said some biochemical patterns related to heart disease and atherosclerosis risk did appear to go back to normal in some patients. "So it is not all bad news," he said.
The professor said the most recent study provided a framework to accurately identify those suffering from long-term effects and what those effects are, which is helpful in developing personalised long-term treatments they may need.
"Now that we have developed an objective metabolic framework for measuring systemic recovery in Covid-19 patients, we can use this to definitively track whether people are in fact fully recovering from the disease," he said.
Further studies with more people are needed to confirm the biomarkers needed for long-term monitoring.
It is not known whether "Long Covid", also known as Post-Acute Covid-19 Syndrome (PACS), is an extension of the disease or marks the start of separate chronic disease driven by the body's enhanced immune response to the virus.
"There are now over 140 million so-called 'recovered' people around the world, so it is possible that long-term effects will be seen in tens of millions of people with significantly increased healthcare economic burdens as well as the individual medical problems," Prof Nicholson said.
The findings from the study — a collaboration with the Covid Research Response Trial led by the University of Western Australia, the ANPC, Spinnaker Health Research Foundation and South Metropolitan Health Service — have been published in a peer-reviewed paper in the Journal of Proteome Research (American Chemical Society).
University of Western Australia endocrinologist Professor Bu Yeap said the research marked an important milestone in delivering better care to those affected.
"The results show that there are persisting metabolic and inflammatory changes in patients after acute Covid-19 infection, which relate to some Long Covid symptoms," Prof Yeap said.
"This is an important step towards better understanding the long-term health impacts of Covid-19, which would help us provide better care for those affected."