>>12373595I'll explain it simply
Humans sometimes get a virus in them. That virus has a particular set of structures. the immune system finds that those structures are on the banned list, and so does some shit to destroy them. After destroying the virus, some cells decide to stick around for a long time, in case virus-chan returns, these are memory cells.
A vaccine provides these structures to your immune system, to make memory cells, without the negative effects of actually getting a virus.
However, the vaccine needs some other chemicals in it for complex reasons, usually chemicals that are part of your diet.
Some people are allergic to certain chemicals though, and so rarely, about 1 in 1,000,000 a person will get an allergic reaction.
An allergic reaction is the immune system having cells that react to a chemical/structure that it shouldn't.
In older vaccines (in the 60s) the vaccine contained killed virus or virus that had similar structures but couldnt infect humans (but infect apes instead, for example). One of the problems was a fuck up in killing the virus, meaning some shots contained a live virus.
Modern vaccines dont contain viruses (living or dead), they contain parts of the structure, or they give the body a way to produce the structure temporarily (mRNA vaccine).
Generally a virus enters you cell, and uses the cell to make its structures. We can use this mechanism for vaccines. We give the cell the information to make a few structures, which then lead to memory cells. But it is done without injecting a virus.
The covid vaccine, if it is ruled safe, will be safe because it leads to memory cells, without giving us the virus, and without causing allergic reaction (except 1 in 1,000,000). Fortunately allergic reaction is quick and easy to treat
