A woman and a baby in Wuhan, China, where the first COVID-19 cases were reported.Credit: Nicolas Asfouri/AFP/Getty

"Long story short, COVID-19 leads to lasting and possibly permanent changes in immune cells in some, but not all people."

"Their white blood cells were unrecognizable compared to healthy donors."

"We've learned that this virus, and we can't tell you how, leads to the death of a whole bunch of T cells, and then seems to, at least in some people, lead to damage to the white blood cells they make after that infection."

"Once a T cell commits to responding to one thing, it can't respond to anything else. As we age, more and more of them become committed to responding to infections, or all the other things we might be exposed to, and fewer and fewer are available to respond to new threats."

"Many, hopefully most people, will be fine. Once you've got T cells committed to the vaccine or the virus, in theory these should be expanded and activated once you are boosted."

Dawn Bowdish, Canada research chair in aging and immunity, McMaster University

It could be that SARS-CoV-2 is remaining in the body and causing immune alterations."

"[Some groups reported people with even mild infections had symptoms of T cell] exhaustion [and people with multiple infections of COVID had] poorer performing immune memory to SARS-CoV-2."

"It was almost as if their T cells were giving up the ghost."

Anthony Leonardi, T cell researcher, Boston

"Much remains to be learned."

"However, I agree with the school of thought that it is preferable to avoid this infection, because of the risks of long COVID and evidence of long-lasting effects."

Immunologist Tania Watts, University of Toronto

A health-care worker tends to a person with COVID-19 in London, where the viral variant B.1.1.7 caused cases to surge.Credit: Kirsty Wigglesworth/AFP/Getty

A new alert has been raised among the community of scientists absorbed in the study of SARS-CoV-2 causing COVID and its short- and long-term effects on the human body and mind. Researchers are facing evidence that repeated infections with the COVID-19 virus may be responsible for premature aging of the human immune system. Ontario public health officials noted recently in an update that evidence is emerging of SARS-CoV-2 causing "immune dysregulation".

This is characterized by an immune system that fails to behave normally. Where it has been observed that white blood cell counts may be degraded, in that immune cells fail to respond in the manner they normally would, and inflammation becomes more troublesome than it should be. New research suggests that T cells that normally aid in the production of antibodies to kill infected cells, have been modified by COVID.

"A potential increase in acquired impaired immunity in the Ontario population could have significant impact on the incidence and associated burden of infectious diseases -- and other conditions in the longer term."

Public Health Ontario brief

A cell infected with SARS-CoV-2 particles (pink; artificiallly coloured).Credit: Science Photo Library

Of concern is that people may be found to be less capable of fending off pathogens and infections like influenza as a result of COVID infections, or that an immune system that has become degraded could lead to an increase in autoimmune diseases such as diabetes. Immune imbalance, which has been recognized as a key feature of long COVID, an issue that intrigued Dr. Bowdish, leading her to examine a blood sample from a hospitalized patient with SARS-CoV-2.

As a result of research by her team, results of a small study has been published indicating abnormal white blood cell counts and high inflammation present even in asymptomatic and mild 'recoverees'. A problem that is seen to be more pronounced in people with severe COVID cases. In some instances it was found that blood cells never fully recover "and seem to generate autoimmune reactions" causing the body's immune system to attack its own tissues.

 

A person with COVID-19 lies in an intensive-care unit in Santiago.Credit: Martin Bernetti/AFP/Getty

Lower numbers of "naive" T and B cells (cells producing antibodies) were found in people who had COVID, in a recent study. Naive cells represent those not yet responding to an infection and therefore not yet dedicated to a single-purpose function. Fewer naive T cells is recognized as a sign of "immune aging", where a level of resilience remains to produce more naive cells "but not an indefinite capacity", points out Dr. Bowdish.

According to one theory, SARS-CoV-2 hyperactivates T cells leading in severe cases to overzealous cells causing chronic elevated inflammation responsible for harm done to the body, according to Anthony Leonardi. A Boston group reported that people with long COVID had persistent bits of spike protein in their blood remaining up to a year post diagnosis, seen as a potential reservoir of infection.

It becomes easier to be reinfected when people with multiple infections of COVID ended up with "poorer performing immune memory to SARS-CoV-2", explained Dr. Leonardi.Vaccines and boosters are seen still to be effective against the risk of severe infections. Most people were found in a review to eradicate the virus, and current vaccines "elicit robust T cell responses that likely contribute to remarkable protection against hospitalization or death", said Dr. Bowdish.

Still, with some people losing naive cells, this may leave them less likely to respond to other viruses or infection "so that's the major concern", elaborated Dr.Bowdish. Persistent inflammation is a troubling sign, one that leads people to be more likely to develop cardiovascular problems or strokes. 

Children play in Israel, where roughly 60% of people have received at least one dose of COVID-19 vaccine.Credit: Guy Prives/Getty