Individual immunity and herd immunity are established by the human immune system. T-cells "learn" to recognize and attack pathogens.
Historically vaccines introduce weakened or inert pathogens to help the body's immune system to recognize and then attack them with minimal to no side effects.
mRNA vaccines are experimental CRISPR tech and have no significant historical data that can evaluate their beneficial efficacy. They introduce genetic material that alters human DNA. It is probably better to say it is DNA russian roulette and, the mutation of the host DNA is probably irreversible. Most mutations are negative and harmful. They are likely to cause "unforeseen" changes… like prion proteins.
In my opinion mRNA vaccines are euthanasia tools intended to drastically reduce human population by causing premature death and significant infertility problems for the human population.