With the coronavirus raging around the world, the immune system became an area of public interest not seen since the early days of the AIDS crisis. The reason this coronavirus has been so problematic for us is because it is “novel”, meaning we have not encountered it before in human history. The result? Our immune systems did not yet know how to recognize or respond to it.
You may have heard the term “herd immunity”. This means that 70-90% of the population have been exposed to an infectious microbe. Usually, the immune system develops a memory of that microbe and the next time it comes around, we respond swiftly to neutralize and destroy it before it causes illness. When enough people in a population have this defense in place, community spread becomes much more difficult, since the microbe has a harder time finding a vulnerable host.
But how does the immune system actually work? The immune system is a complex system of checks and balances. Without getting into too much detail, let’s discuss innate versus adaptive immunity.
Innate immunity refers to the cells of our immune system that are constantly on patrol, looking for threats. This response involves many of the cells of the immune system: natural killer cells, eosinophils, macrophages and more. These cells respond to anything perceived as threatening, to protect us, but they can also become problematic, as in allergic reactions.
The adaptive immune system is comprised of T and B lymphocytes (T-cells and B-cells). These cells respond specifically to different invaders: they are immune cells that learn! Once they have encountered a microbe, these cells will remember it, to fight it off if it appears again in the future.
Covid 19 is an unusual virus in many ways. One way it seems to be different from many other viral illnesses is that it can persist and create a post viral syndrome called Long Covid. Symptoms of Long Covid can appear weeks after the acute viral symptoms seem to have cleared, and it can affect systems that were not affected in the acute illness. Many people are now dealing with Long Covid, and there are currently no pharmaceutical treatments that can help. This is an area of active research, since Long Covid is so prevalent.
With a novel microbe such as Covid-19, we had no adaptive immunity in place. All of us needed to mount an effective immune response to it, but in those people suffering with Long Covid, it appears that the immune response did not resolve the infection. Lingering inflammation, caused by the virus in various systems of the body including the brain, did not clear.
Having a healthy and well-balanced immune system is key when recovering from Long Covid.