It is very clear that many people do not know how vaccinations/immunity work. Vaccinations are not 100 percent guaranteed, so an unvaccinated person carrying a highly contagious disease, such as measles, can infect vaccinated people. They are also a risk for people too young for the shots, or those who can't have them due to medical issues. Vaccines do wear off over time. How many of you are sure you are still protected from shots received 15 to 20+ years ago? You are likely not. An unvaccinated person is a threat to you, too.