Resources from: Public Health England
Being vaccinated not only protects yourself from harmful diseases but also protects others around you who either can't be vaccinated or whose immune system can't produce its own defences to vaccines.
Herd immunity describes how a population is protected from a disease after vaccination by stopping the germ responsible for the infection being transmitted between people. In this way even people who cannot be vaccinated can be protected or people who don't produce an immune response to vaccination.
For example, the bacteria meningococcus and pneumococcus can cause blood poisoning (septicaemia) and meningitis. In most people the bacteria live harmlessly in the throat and do not cause disease, but sometimes they get into the bloodstream leading to these severe infections. They can live harmlessly in the throat of one person but if they spread to someone who is particularly susceptible (such as a young baby) they can cause severe disease. By being vaccinated an individual is not only protected from being infected themselves but they then also cannot pass this infection onto other people, where it may cause severe disease. However, for herd immunity to work a large proportion of the population need to be vaccinated.