• A form of immunity that occurs when a certain level of the population within a community is vaccinated against certain infectious diseases to protect those who may not be fully immunized or cannot be fully immunized.n• Typically it takes 90% of the population within a community to reach herd immunity. This is for each and every vaccine. n• For example 90% of the community should be immunized against Measles, Mumps, and Rubella (MMR vaccine) for herd immunity to be reached.n• Herd immunity may also be called: Community Immunity, Social immunity, or Population immunity