Historically, a live vaccine induces more potent, lasting and broader immune responses than a killed vaccine. The body is seeing the microbe in a way that is much more analogous to a real infection.
The bodys immune system is like any other system of the body. Each of them have their vital function for the human host.
The immune systems goal is to protect the body against invaders either from without, such as microbes, or from within, such as cancers and different types of neoplastic transformation.
The entire purpose of a vaccine is to mimic infection as best you can. Historically, a live vaccine induces more potent, lasting and broader immune responses than a killed vaccine. The body is seeing the microbe in a way that is much more analogous to a real infection.
It's a virus that's easily transmitted from person to person through aerosolized droplets from saliva and other body fluids, ... It is unlike anthrax in that it can be transmitted from person to person and not just a danger by a direct contact.