Your vaccination protects people you'll never meet.
A pathogen needs unprotected hosts. Once enough people are immune, it can't find a chain and dies out locally. The threshold depends on contagiousness R0: measles (R0 about 12–18) needs roughly 95 % immune, flu far fewer. Beneficiaries: infants and people who can't be vaccinated.
Useful: For highly contagious diseases, a small drop in coverage is enough for outbreaks.
Source: en.wikipedia.org