As COVID-19 case numbers continue to climb, an immunology expert has warned against complacency as more and more people develop long COVID in the months after their initial infections.
Federation University immunologist Professor Stuart Berzins said researchers still know little about the prevalence of long COVID and what triggers it - particularly when it comes to COVID's Omicron strains.
"At the moment long COVID is a grab-bag of symptoms that can range from feeling confused or foggy through to a cough that doesn't seem to go away or feeling tired and at the moment (researchers) are still trying to pull apart whether it's one disease or a series of different things," he said.
Those suffering long COVID experience one or more symptoms including fatigue, body aches, lack of energy, breathlessness, cognitive difficulties, anxiety, loss/change of taste and/or smell, heart palpitations and several others that persist at least two months after recovering from the initial COVID-19 infection.
"The problematic thing is long COVID seems to hang around. If you've got symptoms after three months you're very likely to still have them after 12 months and we don't really understand why.
"This has raised concerns that long COVID could become an increasingly prevalent health issue unless we develop new approaches to identify and treat high-risk individuals."
Professor Berzins, who is based in Ballarat in Victoria's Central Highlands, said around five to 10 per cent of people who caught COVID ended up with long COVID but research so far had concentrated on long COVID resulting from infection from the Delta strain, not the current Omicron strain which has caused most infections this year.
Professor Berzins said one of the theories behind why some people developed long COVID was that the initial bout of COVID caused damage in the body that took time to repair, or if the damage was permanent the symptoms could also be permanent.
For some people, long COVID will be a consequence of their infection, so it is important that we remain vigilant about minimising COVID-19 cases and continue research in this area so that long COVID can be prevented or treated effectively- Professor Stuart Berzins
Another theory was that while COVID was associated with infection in the respiratory tissues of the lungs, throat and nose, it also went to other areas of the body where it could remain and cause problems long after the infection has cleared from the respiratory system.
Others suggest that the immune response against the COVID-19 virus can trigger a chronic autoimmune response that can cause neurological damage that leads to a diverse range of symptoms. Long COVID has some similarities with chronic fatigue syndrome, which is also poorly understood and often triggered by a viral infection.
"There's certainly evidence for those (theories) but at the moment they are kind of an educated guess and we don't know for sure."
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Studies have so far shown the severity of the initial infection and the viral load made people more likely to develop long COVID, but that is not always the case with many people who tested positive to COVID but had no symptoms also going on to develop long COVID months later.
What is known is that women are more likely to develop long COVID than men, and obesity is also a significant risk factor.
"For many people, the consequences of catching COVID-19 have been no worse than catching a common cold. For others, COVID-19 can see one or more symptoms persisting months after the infection has cleared their body," he said.
Professor Berzins said more research was needed to compare long COVID resulting from the Delta and Omicron strains.
"Whether different variants confer the same likelihood or symptoms of long COVID is not yet known."
"The studies that have come out now on long COVID are based on the Delta strain. By definition, long COVID doesn't rear its head for a few months, then it's another couple of months before you're sure you've got the condition, then research takes place after that.
"To be honest we know virtually nothing about long COVID from Omicron directly because ... the passage of time hasn't been there."
Professor Berzins said the best defence against long COVID was to avoid contracting COVID-19.
"The high rates of vaccination have seen COVID-19 becoming a mild illness for most people who contract it. This has meant the harsh restrictions required earlier in the pandemic are now relaxed or removed entirely, but variants such as Omicron are so transmissible that community infection rates remain extraordinarily high," he said.
"For some people, long COVID will be a consequence of their infection, so it is important that we remain vigilant about minimising COVID-19 cases and continue research in this area so that long COVID can be prevented or treated effectively."
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