I have had COVID and have colds constantly. Has COVID damaged my immune system? Am I now at risk for other infectious diseases?

So you’ve had COVID and now you’re recovered. You don’t have ongoing symptoms, and luckily it doesn’t seem like you’ve developed COVID for a long time.

But what impacts has COVID had on your overall immune system?

It’s still early. But growing evidence suggests that there are changes in your immune system that can put you at risk for other infectious diseases.

Here’s what we know so far.

A round of viral infections

Over the past winter, many of us have had what seemed like a continuous round of viral illnesses. This could have included COVID, influenza, or respiratory syncytial virus infection. We may have recovered from one infection, only to get another.

Then there is the re-emergence of infectious diseases worldwide such as smallpox or polio.

Could they all be connected? Does COVID somehow weaken the immune system to make us more prone to other infectious diseases?

There are many reasons why infectious diseases emerge in new places, after many decades, or in new populations. So we cannot conclude that COVID infections have led to these and other viral infections.

But evidence is building of the negative impact of COVID on a healthy state of the individual immune system, several weeks after the symptoms have disappeared.

Read more: The latest cases of polio have put the world on alert. Here’s what this means for Australia and people traveling overseas

What happens when you get a virus?

There are three possible outcomes after a viral infection:

1) your immune system clears the infection and you recover (for example, with the rhinovirus that causes the common cold)

2) your immune system fights the virus until it becomes “dormant” and you recover with a latent virus in our bodies (for example, the varicella zoster virus, which causes chicken pox)

3) your immune system fights back, and despite best efforts, the virus remains “chronic”, replicating at very low levels (this can happen for hepatitis C virus).

Ideally, we all want option 1, to remove the virus. In fact, most of us clear SARS-CoV-2, the virus that causes COVID. This goes through a complex process, using many different parts of our immune system.

But international evidence suggests that changes in our immune cells after SARS-CoV-2 infection may have other impacts. It can affect our ability to fight other viruses, as well as other pathogens, such as bacteria or fungi.

Read more: No, the extra hygiene precautions we’re taking for COVID-19 won’t weaken our immune systems

How much do we know?

An Australian study has found that SARS-CoV-2 disrupts the balance of immune cells up to 24 weeks after clearing the infection.

There were changes in the relative numbers and types of immune cells among people who had recovered from COVID compared to healthy people who had not been infected.

This included changes in the cells of the innate immune system (which provides a non-specific immune response) and the adaptive immune system (a specific immune response, directed at a recognized foreign invader).

Another study focused specifically on dendritic cells, the immune cells that are often considered the body’s “first line of defense.”

The researchers found fewer of these cells circulating after people recovered from COVID. Those that remained were less able to activate white blood cells known as T cells, a critical step in activating antiviral immunity.

Fewer dendritic (red) cells circulated after COVID.

Other studies have found different impacts on T cells and other types of white blood cells known as B cells (cells involved in antibody production).

After infection with SARS-CoV-2, one study found evidence that many of these cells had been activated and “exhausted.” This suggests that the cells are dysfunctional and may not be able to adequately fight a subsequent infection. In other words, the sustained activation of these immune cells after a SARS-CoV-2 infection may have an impact on other inflammatory diseases.

A study found that people who had recovered from COVID have changes in different types of B cells. This included changes in the cells’ metabolism, which can affect how these cells function . Since B cells are critical for making antibodies, we are not entirely sure of the precise implications.

Could this influence how our bodies produce antibodies against SARS-CoV-2 if we encounter it again? Or could this affect our ability to produce antibodies against pathogens more broadly, against other viruses, bacteria or fungi? The study didn’t say that.

Read more: Explained: What is the immune system?

What impact will these changes have?

A major concern is whether these changes may affect the way the immune system responds to other infections, or whether these changes may worsen or cause other chronic conditions.

Therefore, more work is needed to understand the long-term impact of SARS-CoV-2 infection on a person’s immune system.

For example, we do not yet know how long these changes in the immune system last and whether the immune system recovers. We also do not know whether SARS-CoV-2 triggers other chronic diseases, such as chronic fatigue syndrome (myalgic encephalomyelitis). The investigation into this is ongoing.

What we do know is that having a healthy immune system and getting vaccinated (when a vaccine has been developed) is critical to having the best chance of fighting off any infection.

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