system
Given the following post, respond as if you're commenting on Reddit:
human
Is it possible for the human immune system to "forget" any pathogen after vaccination as time passes? How does this work considering that information on certain pathogens are also retained by the immune system and does this vary based on different pathogens?

If my understanding is correct, after being vaccinated, the body produces antibodies against a particular pathogen. This can offer protection to the body if any live pathogen were to attack the body.

But, and contextually in case of COVID-19, I have also read that, even after vaccination, the antibodies that target the virus drop in number with the passage of time. Contrary to this, I have also read that the immune system does have the ability to remember and retain information about any pathogen for extended periods of time. How do these two correlate with each other?

Does/Can the human immune system essentially forget the information on any pathogen after a set period of time? Is this universal to all pathogens and if not, what exactly affects this?
gpt
When a person is vaccinated, a pathogen protein/inactivated pathogen/weakened pathogen containing foreign proteins is delivered into their body (or as is the case for new generation of vaccines, a pathogen's protein is produced in vaccinated person's body)

Such protein is recognised as foreign by lymphocytes: B cells and T cells; as B cell response is somewhat easier to explain and responsible for production of antibodies, we will concentrate on it.

Upon contact with such foreign proteins and with the help of other cells, B cells start to mature and attempt to produce antibodies than have high affinity for (attach strongly to) foreign proteins. Some of those B cells that succeed in producing those high affinity antibodies will become plasma cells and will produce high amounts of antibodies but will eventually stop and die without continued stimulation by foreign protein. That's why the antibody levels will fall - unless contact with foreign protein is repeated.

However, some B cells become memory B cells. Those are not very active but they do have the ability to produce antibodies with high affinity for the foreign protein once activated by a particular pathogen protein. Should contact with pathogen be repeated, they will become active and some will become plasma cells that produce large amounts of antibodies. Memory B cells may last for decades in their inactive state.

Generally speaking, it is very beneficial for us to have the ability to mount a swifter immune response in case of repeated contact with antigene. However sometimes, it's not just the memory that would be useful but also high antibody levels and they generally fall over time.

To conclude: human immune system retains the ability to produce antibodies against a pathogen for decades, but unless stimulated again, the levels of those antibodies will gradually fall.