With the vaccine hesitancy being as prevalent as it is now, I think more than one of you have had someone in their immediate environment be vaccine-skeptical or at least vaccine-hesitant.
Here is an explanation that worked for someone from my family, helping them to transit from a “I don’t need it – I am healthy enough” mindset to “Ok, I am getting the vaccine ASAP”. In this particular case, the fact that they had several friends go to hospital due to COVID and in some cases be long-term incapacitate by COVID19 helped to raise awareness of how bad the disease can be, as well as underlying trust into my competence as well as a good will, with most of hesitation focused around “my natural immunity is already good” and “vaccines don’t work that well to start with”. Oh, and also the simplifications are pretty insane and I can hear immunologists and virologists scream for here, but it’s one of those “sacrifice precision for ease of understanding” cases.
So, the preamble being done, let’s get to the actual explanation:
“Your immune system works by learning what attacked you and takes time to react. Specifically, it looks for cells that explode and let their contents out (also called necrosis, as opposed to apoptosis-when the cell dies because it is programmed to by the organism) and starts looking for anything it would have not encountered before (or at least that it doesn’t encounter in the organism often) that is present in the contents of the exploded cell or around. When the immune system detects what is there, they start generating the antibodies and test all the cells in the organism to see if they contain the new dangerous compound (here it is particles of the virus). If the dangerous compound is present in the cells, the immune system orders “cleaner” cells to digest those cells and destroy them and everything they contain.
The problem is that the process starts only when there are first mass cell deaths (so the infection is well stated) and take several days to start and spin-up. During that time, the virus continue to propagate in the body.
So when the cleaning cells start digesting cells that have the virus in them, that’s a lot of cells. And some of them are very important and cannot be replaced – such as heart cells. Or some cells that can be regenerated, but if there are too much that die, you die as well (a good example are lung cells).
In case of the vaccine, you have proteins that are located on the outside of the virus that are injected, as well as an agent that will provoke the cells to explode and attract the immune system’s attention. So the immune system will detect the viral proteins “on the crime scene” and learn to find and destroy them on sight. But since there are not that many cells that are affected and are very easy to regenerate (muscle cells are among the easiest to regenerate – you actually regenerate a lot of them every day if you are exercising) and are not essential to life (given it’s a muscle of a hand and not heart/lungs/brain).
Once your immune system learnt to detect them, it will remember them for a long time and closely monitor your body to see if it can find the smallest traces of the particles it learned were dangerous, even before the first infected cell explodes. Your immune system will monitor your body even closer and longer for those particles if it finds those particles on a different “scene of crime’. That’s why we need a second dose of the vaccines.
So when the virus arrives, it is immediately detected and neutralized and cells it has the time to infect are destroyed before they explode and before the virus is able to replicate itself.
The reason we need to wait after a vaccine is that the immune system transits from a “I am currently responding to an attack” to a “I have responded to an attack and will remember what attacked me, so that the next time I can respond faster and better”. That process takes about 10-14 days, but 21 days leave a margin if the immune system doesn’t work all that great (for instance if the person is stressed).”
Now, as to the need to get vaccinated immediate, the argument went along the lines that with countries opening up, barriers for the virus propagation are going down and we are still very far from herd immunity, meaning your own vaccine is the only thing that will be protecting you, with everyone not yet vaccinated getting sweeped in the upcoming wave.