Vaccination protects the person who receives it, but its wider effect reaches further. When enough people in a community are immunised, a disease loses the chain of contact it needs to spread, which means even people who cannot be vaccinated, for medical reasons or age, gain a measure of protection too.
This effect, often called herd or community protection, is really just an extension of everyday logic: a fire spreads more slowly through a room with fewer flammable objects. Fewer susceptible people means fewer opportunities for a pathogen to pass along, and outbreaks that might once have spread widely instead fizzle out early.
It is a quietly collective form of health, one where an individual choice becomes a small contribution to everyone else's safety. That is part of why public health has always treated vaccination as a shared project rather than a purely private decision, worth explaining patiently rather than assuming everyone already understands.