Herd immunity is a way to protect a whole group of people from a virus or disease. Often this is done by vaccinating a large percentage of the population. Herd immunity is a way to protect those at increased risk from a disease, such as the Elderly, children, or those who are immunocompromised. It also protects those who can’t get immunized themselves, such as those allergic to the vaccine. Once herd immunity is reached, it is still possible for outbreaks to occur, but they are generally on a much smaller scale.