Long COVID: Hit to immune system lingers for months after infection

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Unvaccinated people are at much higher risk of experiencing the debilitating effects of long COVID, with a major study revealing the hit to the immune system lingers months after infection even with mild illness.

Researchers from St Vincent’s Hospital and University of NSW’s Kirby Institute have for the first time found elevated inflammation levels in unvaccinated people who caught the virus during the state’s first wave, indicating abnormalities in the immune system persist at least eight months after recovery.

“Symptoms of long COVID, from fatigue to headache, are a real phenomenon,” Professor Gail Matthews said, the head of infectious diseases at St Vincent’s and one of the study’s senior authors. “What has really been lacking – until now – is hard biological evidence of something being wrong.”

Simon Strum contracted coronavirus in June 2021 during NSW’s Delta wave. He now has long COVID.Credit:Rhett Wyman

“Many long COVID sufferers have felt disbelieved. And, so far, there has been a lack of good evidence to dispute that.”

The study, published in Nature Immunology, examined multiple blood samples of 62 Australians diagnosed with coronavirus in the first six months of 2020. It found a spike in interferons in those with long-lasting symptoms, the proteins in cells which fight viral infection.

It used data collected from St Vincent’s Hospital’s ADAPT study. There was no vaccine available at the time.

“You would expect that after the virus has gone, and a patient has recovered, that the immune system would settle down. But it didn’t, it continued to be over-active months after,” co-lead author Chansavath Phetsouphanh and senior research associate at the Kirby Institute said.

Dr Phetsouphanh said the research team analysed 29 different biomarkers, or proteins, that they suspected could be triggered by having been exposed to the virus.

Interferons generally disappear after an infection clears, but in patients with long COVID high levels of interferons continued for months compared to those without extended symptoms.

“These elevated interferons can lead to fatigue, depression, headache and other long COVID symptoms,” Dr Phetsouphanh said. “One of the most surprising aspects of our analysis is that people don’t need to have had severe COVID to experience these ongoing immunological changes, this occurred in people with mild and moderate disease.”

For more than six months, Simon Strum has been plagued with symptoms – fatigue and loss of balance – that have proved difficult to ignore.

Mr Strum, 50, contracted COVID-19 as the Delta wave took off in Sydney in late June, and spent two days in St Vincent’s followed by months at home in recovery. He had not yet been vaccinated when he caught the virus.

“It was an intense week of high fevers, chills, muscle pains, headaches, loss of taste and smell. Then a cough that never-ended and about six weeks later I started to have problems with balance,” Mr Strum, who was not part of the study, said.

“I have had months of being dizzy, loss of balance, am forgetful and have brain fog. Even if your symptoms are mild or you are asymptomatic you just don’t know how it will affect you in the long run,” Mr Strum said, noting before catching the disease he was fit and would regularly take 10 kilometre walks near his Bondi home.

Study co-author Greg Dore said it was difficult to understand how widespread long COVID will be given the now high rates of vaccination and the emergence of Omicron, which is less severe and virulent than previous strains.

“Our hypothesis is that small remnants of the virus or an autoimmune-type disorder are enough to trigger an immune activation which can lead to ongoing symptoms,” Professor Dore said.

“With an enormous wave of Omicron cases, even with a variant that is less severe, a small proportion of those with long COVID could translate to considerable disease burden. We will know more about Omicron’s impact on long in COVID in the next three months.”

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