The vaccine is the covid virus itself. The scientists have made it to become weaker as if it was already dead. And when this vaccine gets vaccinated to a person, that person's immune system will be able to defeat the virus since it has become weaker already. So after being vaccinated, the person who was already vaccinated will have lesser chance of being infected or dying from the virus since the immune system is now aware of the existence of the covid-19 and have now acquired the knowledge on how to defeat it.
* Correct me if im wrong *
