A new study from Australia reportedly provides insight into the lasting effects of COVID-19 on immune system activity. The study, which tracked various biomarkers, found that immune abnormalities persisted for at least six months after recovery in COVID-19 patients.
Eighteen months into the global pandemic, researchers are increasingly investigating the long-term effects of SARS-CoV-2 infection – “long COVID” – with a growing number of patients reporting persistent symptoms that last for months after acute illness.
The Australian study is following 69 recovered COVID-19 patients, most of whom (47) had only mild symptoms. Because of Australia’s unique location in the world, where the virus has been temporarily eliminated in some areas, ongoing projects can track long-term immune responses to infection without fear of reinfection or vaccination status.
The new study, which has not been peer-reviewed or published in a journal, outlines the impact of the infection on the peripheral immune system for six months after initial recovery. During the six-month study, blood samples were collected from each subject at three sites.
Researchers investigated levels of about 130 different immune cells, as well as tracking antibody responses and measuring the expression of thousands of different genes related to immune function. The results of the study showed strikingly that inflammatory responses and immune dysregulation persisted for six months after recovery.
“This study found that substantial dysregulation of immune cell counts was strongest at 12 weeks post-infection, but remained evident in most cases for up to six months and possibly longer,” explained David Lynn, one of the project’s principal investigators. Six months after infection, a number of genes associated with inflammation were found to be upregulated. This suggests that these dysfunctional immune mechanisms may be part of the mystery of LONG COVID, however, Lynn is clear that further research is needed to test this hypothesis.
“One could logically infer that this dysregulation is associated with the physical symptoms of LONG COVID, however, further research is needed to prove this,” Lynn added.
This new study is part of a growing body of evidence linking abnormalities in the immune system to the pathology of long COVID. a British study published in April detected persistent immune alterations in hospitalized COVID-19 patients six months after discharge from hospital.
However, this Australian study looked at a variety of COVID-19 cases, ranging from mild to severe. And one of the biggest surprises in the new findings was the lack of any association between the severity of acute disease and the degree of immune dysfunction following infection.
We’ve seen a very wide range of recovery rates, and we still don’t understand why some people recover more quickly than others,” Lynn said. The severity of the disease doesn’t directly translate to the degree of immune dysfunction, and we haven’t been able to find any pattern that suggests a person’s age or gender is a distinguishing factor governing differences in recovery.”
A limitation of this Australian study is that there are no data tracking symptoms of LONG COVID in the cohort, so these findings cannot be directly linked to LONG COVID cases. But the immune dysfunction/long COVID hypothesis is becoming more plausible.
Danny Altmann, an immunologist at Imperial College London who is involved in a large ongoing UK project to investigate LONG COVID, says there is precedent for viral infections triggering long-term chronic health conditions, and glandular fever is a perfect example. And these chronic conditions may be associated with lingering immune dysfunction following acute infection.
In a recent interview, Altmann explained, “I would describe it as sort of like someone threw a grenade at our immune system and all the (immune cell) populations were completely upside down and unsettled for years. And, it’s just a guess, but we’ve got the technology to look at this in quite a bit of detail.”
Branka Grubor-Bauk, the Australian researcher working on the new study, suggested that there is an urgent need to better understand LONG COVID, especially given that the virus doesn’t appear to be going away.
Grubor-Bauk said, “There are currently no treatments for people with long COVID, and as the world slowly transitions to living with COVID, we will need to find answers and better solutions to prevent and treat long COVID in the years to come.”
The new study has not yet been peer-reviewed, but it has been published on the preprint platform medRxiv.