Does COVID-19 make you more susceptible to the flu, other viruses? Scientists weigh in

If you’re feeling fatigued from a recent COVID-19 infection, some speculate that your immune system may be exhausted too.

Canadians are anecdotally reporting catching the flu or even a stomach virus soon after recovering from COVID-19, making them wonder if their immune system has been weakened.

An immunologist and York University professor says it’s a fair assumption.

“The reason people are interested in this is that there was this initial fear that ‘Oh we’re going to have a twindemic‘ – the flu plus COVID. But that never materialized,” Ali Abdul-Sater told Global News via Zoom.

That means the country did not see an alarming spike in flu cases during this season … and some health experts suspect that may have a lot more to do with masking and physical distancing as opposed to the strength of people’s immune systems.

Still, many say they got a bad case of sniffles following COVID. Dr. Doug Manuel said that is probably an outcome of being cooped up at home for a long time, and those masks coming off.

“We are concerned that we have now had a few years where people haven’t been exposed to RSV or influenza, and so now our immunity is a little bit lower for those,” the director of the Wastewater Surveillance Group with CoVaRR-Net, and senior scientist with The Ottawa Hospital told Global.

Does that mean the weakened immune system theory is completely out the window?

“We don’t really have enough data on (whether or not COVID is) really weakening our immune system,” said Dr. Angela Cheung, a professor with Temerty Faculty of Medicine at the University of Toronto, and a Senior Clinician Scientist with University Health Network.

Abdul-Sater says weakened immunity post-disease is something that is widely studied, but has been vaguely looked at with MERS and other coronaviruses.

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Some literature suggests a decreased level of lymphocyte immune cells following an infection. However, another kind of immune cells – innate cells – shoots up.

This doesn’t necessarily suggest your immune system is either weaker or stronger, Abdul-Sater said. Complex factors such as age and the severity of the disease have to be taken into account.

“Short-lived infections generally don’t tend to cause significant or long-term dysfunction to the immune system. But viruses that cause chronic infections – so hepatitis C, hepatitis B, HIV – certainly cause significant dysfunction,” he said.

Despite this, Manuel said scientists are “open-minded” to the idea that COVID-19 may actually be debilitating to the immune system.

While also questionable due to limited studies, there is literature that suggests COVID-19 may cause ‘immune dysregulation’ similar to how HIV and hepatitis C do.

Almost like a short-circuit, Cheung describes immune dysregulation as your immune system just not functioning the way that it should.

One such example? “Your body produces antibodies fighting your own body, your own cells,” she said.

This was highlighted in a 2020 German case report of recent studies. It details COVID-19 patients suffering Guillain-Barré Syndrome, a condition where immune cells attack the nerves, potentially causing paralysis.

Other studies suggest COVID-19 may cause your immune system to mobilize excessively against the virus in a so-called “cytokine storm”  – causing dangerous, sometimes deadly, levels of inflammation.

Cheung, who is also the director of the Women’s Health Program at the University of Toronto, said immune dysregulation seems to affect more women than men. But she stresses that studies are in “really early stages.”

Some scientists are also researching a possible connection between long covid and immune dysregulation, which Abdul-Sater and Cheung say also remains unclear.

From an immune standpoint, some symptoms, like exhausted immune cells, match up to those of long COVID. But others like brain fog, concentration difficulties, and breathing problems, Abdul-Sater said, do not.

Definitive insight on those theories will take time, said Cheung, as emerging variants complicate the situation.

But Abdul-Sater thinks that kind of research will take a front seat now, as scientists begin to look beyond the immediate effects of the deadly virus.