His team's research has shown that even people who experienced only mild symptoms with earlier variants of Covid-19 were at risk of developing Long Covid and he thinks it likely further study will find the same is true of Omicron.
Most people, Nicholson says, think of Covid-19 as a respiratory disease, which it is, but part of the body's defence against the disease is an immune response.
"It turns out with Covid-19, in particular, there are lots of other body systems that get affected by the infection and it's not ... necessarily the infection of those other organs or tissues, it's the immunological interaction with those other tissues [that can cause longer-term problems]."
"So you can have a respiratory infection, and your body can fight it off, but the immune processes involved in fighting that off - in some people, not everybody - can cause these systemic effects which then persist for a long time, either symptomatically, or asymptomatically," he says.
"My guess is [Omicron] won't produce as much Long Covid as the earlier variants, but it still will happen."
When Covid-19 first emerged a little over two years ago, Nicholson's first thought was to look at what was known about the most-similar existing disease, SARS-CoV-1, which caused the original Sars disease in the early 2000s.
He says of the roughly 1000 people who contracted that disease, 50 percent of those who survived were still suffering long-term effects 15 years on.
Covid-19, he says, appears to be behaving similarly.
"Other viral diseases can cause long-term effects ... but Covid seems to be very good at doing it even when the disease is quite mild, and that's what sets it apart."
His team is working with multiple universities around the world - including Harvard and Cambridge - to try and understand the long term cardiometabolic and other systemic effects of Covid-19, as well as the impact of the disease in children.
Among their findings are a new set of biomarkers for increased risk of cardiovascular disease in patients with Covid-19 infections.
In fact, it was the discovery of these biomarkers that helped him to realise he had contracted Covid-19 himself.
Following a trip to Italy in February 2020, Nicholson believed the lingering fatigue he was experiencing upon his return to Australia was just jetlag.
When he continued to feel tired several weeks later he went to his GP and got "tested for everything", though in early March 2020, no test for Covid-19 yet existed.
The tests revealed he had diabetes, some abnormal liver function and "a few other bits and pieces, but no infection of any sort that could be detected".
It wasn't until his team began building the diagnostic tests for Covid-19 biomarkers and he submitted to a test himself that he had any inkling he may have had the disease.
"My biochemistry was like [that of] a Covid patient and this was three or four months after I'd actually had the episode (of fatigue)," he says.
Subsequent antibody testing confirmed he had been exposed to Covid-19.
"We detected it in my own laboratory using our own tests and I wasn't one of the controls, I was one of the patients!"
Nicholson's experience gave him an early insight into the fact that people who contract Covid-19 could still be suffering biochemical abnormalities months after their initial infection with the disease.
But more than that, it highlighted just how much a Covid-19 infection can impact a person's biomarkers for cardiovascular risk.
He says his team's research has shown that those who have been infected can see their cardiovascular risk biomarkers increase dramatically, doubling, quadrupling or even increasing 10-fold during the acute phase of their infection.
"Some people seem to completely recover that risk at a year (post-infection)," he says, while other people don't.
"I'm pleased to say that my cardiovascular risk has gone back to pretty much normal now, whereas it was about four-fold elevated in the first year after I'd had Covid."
Covid-19 infection "does absolutely increase the risk of heart disease", he says, citing a large study published in Nature Medicine in February, which found even mild cases of Covid-19 increased a person's risk of cardiovascular problems a year after diagnosis.
The more severe a person's symptoms were during the acute phase of their infection, the more likely they were to have some increased cardiovascular risk, the paper found, though Nicholson said it was particularly concerning that even those under 65 with no other risk factors were shown to have an elevated risk over the background population of having some sort of cardiovascular event a year on.
"That's really quite extraordinary," he says. "The studies for cardiovascular risk are absolutely conclusive and this is over and above what you would expect for normal, critical care patients."
Another concern is the long-term impact of Covid-19 in children who contract it.
While kids tend to experience fairly mild symptoms during the acute phase of an infection, "their blood biochemistry is really quite abnormal", Nicholson says.
A study his team is undertaking with Harvard University on paediatric Covid-19 has found about 1 percent of children are developing a related disease called multiple inflammatory syndrome in children (MIS-C) two to three months after their Covid-19 infection.
MIS-C particularly affects the gut and the heart, Nicholson says, and mostly the children recover, but it's unknown what the longer-term risk of them then developing other things like diabetes or cardiovascular disease is.
"The knowledge that children still are metabolically quite badly affected, even if they're not coughing, means that we have to be very careful," he says.
"We should vaccinate them ... there is no good reason for not doing it, as far as I can see, and there are lots of good reasons for doing it just because we're ... potentially reducing the long-term risks of them catching the disease."
Nicholson says there is much still to be discovered about Covid-19, which he describes as an "enigma" in terms of the range of biochemical and organ effects that it causes.
"I've spent 30 years in this game and I've never seen a disease that produces such a range of effects as Covid-19, so it's all there to be discovered."
>- RNZ
