What affect do mutations to pathogens have on the effectiveness of vaccinations, and why is this important?

Mutations of pathogens produce new strains. Vaccinations may no longer be effective against these new strains. Vaccinations would kill non-resistant strain pathogens. However, resistant strain pathogens would survive and reproduce. This would cause the population of the resistant strain to increase. The resistant strain would spread rapidly because there is no effective treatment and people are not immune to it. Using antibiotics to treat non-serious infections, such as colds, can select for resistant strains of pathogens. Due to this, antibiotics are no longer used to treat non-serious infections in the UK