Is COVID harming immune systems? Here’s what we know, and what we don’t

A surge of viral illness across Canada, especially among children, has sparked questions among some infectious diseases experts about whether COVID-19 is damaging the immune systems of its patients and making them more susceptible to other illnesses.

But while there might be some evidence that COVID-19 is having an effect on some patients’ immune cells, it turns out there is still not enough data to definitively say SARS-CoV-2 is damaging every infected person’s immune system. There is even less evidence available to say COVID-19 is responsible for the current wave of respiratory illnesses that are swamping hospitals and ERs across Canada, according to some experts.

The question of whether the novel coronavirus is weakening immunity has been raised in a number of public forums in recent months as a theory that could explain not only why so many Canadians – notably young children – are contracting influenza, respiratory syncytial virus (RSV) and other viral illnesses across Canada, but also why many children are experiencing more severe illness than normal for these viruses.

Children’s hospitals across the country have been reporting record high numbers of patients in their emergency, intensive care and hospital units. The issue is so pronounced in parts of Ontario that a number of major children’s hospitals in the province have had to cancel non-urgent surgeries in order to redeploy staff to ERs and ICUs that are operating beyond capacity.

The situation is similar across the country, with children’s hospitals in Nova Scotia, Quebec, Manitoba, Saskatchewan, Alberta and British Columbia all reporting surges in patients – a situation that is adding significant strain to provincial health systems that were already cracking under the pressures of health worker shortages before the viral outbreaks.

Colin Furness, an infection control epidemiologist and assistant professor in the faculty of information at the University of Toronto, told Global News last week he believes COVID-19 may be partly to blame for the sudden surge of severely ill children, due to emerging evidence from some preliminary studies showing that COVID-19 harms the immune system.

“We know that COVID blocks the production of interferon, which is a red flag that cells wave when they’re being attacked. We know that there are other kinds of immune system impairment with COVID, and it’s going to take a little while to really try and explain that more clearly,” he said. “But it seems to be what’s going on, and it certainly fits the facts.”

Furness did stress, however, that it isn’t yet clear how much damage COVID-19 may be doing and what long-term effects this could have.

Dawn Bowdish, a professor of medicine and a Canada Research Chair in aging and immunity at McMaster University, has been studying the impact of COVID-19 on immune function and says there is evidence that the virus is affecting immune cells, known as T-cells, for reasons that are not fully understood.

T-cells are a type of white blood cell that protect the body from infection.

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People who have a severe COVID-19 infection often see a large drop in the number of T-cells in their body and some of these patients don’t see these T-cells return in the same ways, she said. But how this affects each patient can be very different, including among people who develop long COVID, she added.

“Some people develop a very autoimmune phenotype,” she said.

“But when people don’t have long COVID, it’s those people in the middle, the people who maybe had disease that wasn’t severe enough to land them in the hospital, that are really the ones that are quite intriguing because some of them appear to have some immune changes and others seem to be fine.”

One of the many things that remains unclear is how important these changes to the immune system are in the long run, Bowdish said.

There is a growing body of evidence showing that COVID survivors, even those who have only suffered a mild infection, are more likely to experience heart attacks, strokes and that they are more likely to visit their family doctors for unrelated ailments including mental health disorders, she said.

But whether this is due to immune changes or possible other harms done to the body during infection or for other reasons entirely is “completely unknown right now,” Bowdish said.

“One of the most important things (the evidence gathered to date) tells us is that this virus is not benign. Even if you have a mild infection, it still has the possibility of making you less healthy,” she said.

“What we need to know is how much of this is due to some of these immune changes and how much is due to other things.”

Dr. Sameer Elsayed, an infectious diseases physician and medical microbiologist at London Health Sciences Center and St Joseph’s Hospital in London, Ont., also believes caution should be exercised before jumping to conclusions about COVID-19’s impact on the immune system.

While there is some evidence linking long COVID with overactivity of the immune system, which can prompt some autoimmune responses (in which the body attacks its own healthy tissues), there are a lot of variables that can contribute to immune changes after any illness, said Elsayed, who is also a professor of medicine, pathology and laboratory medicine, epidemiology and biostatistics at Western University.

This makes it impossible to definitively say the coronavirus is causing long-term harm to the immune system and that this is what is triggering so much illness in the community right now, he said.

“There’s still a lot of unknowns because these are just theories right now and we don’t really have the scientific evidence to back anything definitive in this regard.”

A number of small studies and pre-studies have been published in different parts of the world, including some that have not yet been peer-reviewed, showing some linkages between immune “dysregulation” or immune “exhaustion” that can persist in patients months after they recover from COVID-19, including a number that have identified a drop in T-cells.

But these are mostly “observational studies,” Elsayed notes, which don’t always take all possible evidence and factors into account and therefore could be subject to bias in their conclusions.

And while it remains unclear whether some of the evidence that has emerged showing COVID-19’s effect on immune cells is directly to blame for the spike in viral illness in Canada, both Elsayed and Bowdish believe the relaxing of public health measures such as masking is almost certainly playing a role.

As for why so many children are getting sick in such high numbers and are experiencing severe illness to the point of needing hospitalization, Dr. Katharine Smart, past president of the Canadian Medical Association (CMA), says she believes this has been triggered by a combination of many things happening simultaneously.

Masking, home learning and other pandemic measures meant three cohorts of children were not exposed to typical “endemic viruses” like flu and RSV over the last three years, which means they have not had the opportunity to build strong immunity to these illnesses, she said.

That only 7.3 per cent of children under age five have received at least one dose of a COVID-19 vaccine in addition to low numbers of children getting their flu shots so far this year are also contributing factors, Smart added.

“And of course, this is all happening as we backed off of public health measures,” she said, noting that few people are wearing masks anymore, kids are back in school and daycare, and more people are mixing indoors now that the weather is cooler.

“When you pull all that together, I think we’re seeing just a dramatic increase in children presenting with viral illnesses all at the same time. And unfortunately, it’s really overwhelming the capacity in our health-care system right now.”