Do vaccines prevent sepsis?

Certainly! Vaccines are distinct biological triggers that "teach" our immune systems how to prevent and fight specific bacterial or viral illness without actually becoming ill from the pathogen. Vaccines for meningicoccus, pneumococcus, and h. Influenza infections do an amazing job of preventing catastrophic life-threatening illness such as sepsis and meningitis--often working quietly even w/o our awareness.
Possible. There are vaccines available against certain organisms. If one is vaccinated, they may be protected against those particular pathogens that they were vaccinated for.