system
Given the following post, respond as if you're commenting on Reddit:
human
Why does it take two weeks post vaccination to create immunity? What is happening at the cellular level?

I've seen general answers to the question but I'm looking for a specific one. What are the cells produced after vaccination (macrophages, neutrophils, b-cells, t-cells, memory b and t cells, etc) and when are they produced? How do these cells degrade over time, and how do we retain the immunity?

I was curious about this question because we need two weeks post vaccination to develop full immunity. Why is there such a long lag time? Which of these immune cells needs the longer time in order to be produced?
gpt
You make many hundreds of thousands of different antibodies, but the human genome only has about 20 thousand genes. How then, can you make such a diverse range of antibodies which outnumber all the other genes in your body?

The solution is that each BCell is created with a unique antibody gene by doing some copy/paste and adding/deleting random bases of DNA to make it's own antibody. When you are vaccinated, the BCells which happen to make an antibody which weakly binds to the vaccine are activated. They then replicate themselves many times over, and introduce mutations in each daughter cell. The daughter BCells which bind more strongly to the vaccine then reproduce, and create new mutations. What happens over those two weeks is your BCells evolve a highly specific antibody to bind to the target, and then reproduce to high enough numbers that they can create a huge quantity of antibody to flood your body and protect it.

Some of them go on to become memory BCells, so they can reactivate if you get infected again.