So you had COVID and are now recovered. You have no ongoing symptoms and luckily you don’t seem to have developed with COVID for long.
But what effect does COVID have on your overall immune system?
It is still early. But mounting evidence suggests 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
This past winter, many of us seemed to have had a continuous round of viral illnesses. This may have included COVID, influenza, or respiratory syncytial virus infection. We may have recovered from one infection only to get another one.
Added to this is the global resurgence of infectious diseases such as monkeypox and polio.
Could this all be related? Does COVID somehow weaken the immune system to make us more susceptible to other infectious diseases?
There are many reasons why infectious diseases appear in new places or in new populations after many decades. So we cannot conclude that COVID infections led to these and other viral infections.
However, there is evidence of the negative effects of COVID on a healthy person individual immune system, several weeks after the symptoms have subsided.
What happens if you catch a virus?
There are three possible consequences after a viral infection:
- 1.Your immune system clears the infection and you recover (for example, with a rhinovirus that causes a cold)
- 2.Your immune system fights the virus in ‘latency’ and you recover with a virus that’s dormant in our bodies (e.g. the varicella-zoster virus that causes chickenpox).
- 3.Your immune system struggles, and despite your best efforts, the virus remains ‘chronic’, replicating at very low levels (this can occur with the hepatitis C virus).
Ideally we all want option 1 to get rid of the virus. In fact, most of us are eliminating SARS-CoV-2, the virus that causes COVID. It does this through a complex process that uses many different parts of our immune system.
However, international evidence suggests that changes in our immune cells following SARS-CoV-2 infection could have other effects. It can affect our ability to fight other viruses, as well as other pathogens such as bacteria or fungi.
how much do we know
An Australian study has found that SARS-CoV-2 alters the balance of immune cells up to 24 weeks after clearing the infection.
There were changes in the relative number and type of immune cells between people who had recovered from COVID compared to healthy people who were uninfected.
These included changes to cells in the innate immune system (which provides a non-specific immune response) and the adaptive immune system (a specific immune response that targets a recognized foreign invader).
Another study focused specifically on dendritic cells — the immune cells often thought of as the body’s “first line of defense.”
Researchers found fewer of these cells circulated after people recovered from COVID. Those that remained were less able to activate white blood cells known as T cells, a crucial step in activating antiviral immunity.
Other studies have found different effects on T cells and other types of white blood cells known as B cells (cells involved in producing antibodies).
After SARS-CoV-2 infection, one study found evidence that many of these cells were activated and “depleted.” This suggests that the cells are dysfunctional and may not be able to adequately fight off subsequent infection. In other words, sustained activation of these immune cells after SARS-CoV-2 infection can have implications for other inflammatory diseases.
A study found that people who had recovered from COVID show changes in different types of B cells. These included changes in the metabolism of cells that can affect how those cells function. Because B cells are crucial for producing antibodies, we’re not entirely sure of the exact implications.
Could this affect how our body produces antibodies to SARS-CoV-2 should 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.
What impact will these changes have?
One of the main concerns is whether such changes affect the immune system’s response to other infections, or whether these changes could worsen or cause other chronic diseases.
So, more work needs to be done to understand the long-term effects of SARS-CoV-2 infection on a person’s immune system.
For example, we still don’t 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). Research on this is in progress.
What we do know is that a healthy immune system and vaccination (if a vaccine has been developed) are vital to have the best chance of fighting off an infection.
Lara Herrero is Research Associate in Virology and Infectious Diseases at Griffith University. This piece first appeared on The Conversation.