When a large portion of a community gets vaccinated they create a herd of immune people around those who are unable to be vaccinated, such as people with compromised immune systems, infants, and pregnant women.
By having a high number of vaccinated people in the community, these people who aren’t able to get their vaccines are more likely to be protected from disease.
You may think that if your child is left unvaccinated they will be protected by the herd. Well…how many other parents have thought the same thing?