Herd immunity or population immunity

• A population with a high number of members with immunity to a particular disease or pathogen may give protection from that infection to the small number of its non-immune members. This is as a result of there being too few susceptible persons in the “herd” for the infection to circulate. This is known as “herd immunity or population immunity.”

• Immunization OR Active immunity of children can go well beyond saving individual lives. It can also help in preventing largescale outbreaks of diseases as well as keeping a disease under control (or sometimes even eliminated or eradicated e.g. polio) in the area.

• Innate immunity - We are all born with some level of immunity to invaders. Human immune systems, similarly to those of many animals, will attack foreign invaders from day one. This innate immunity includes the external barriers of our body — the first line of defense against pathogens — such as the skin and mucous membranes of the throat and gut. This response is more general and non-specific. If the pathogen manages to dodge the innate immune system, adaptive or acquired immunity kicks in.

• Adaptive (acquired) immunity - This protects from pathogens develops as we go through life. As we are exposed to diseases or get vaccinated, we build up a library of antibodies to different pathogens. This is sometimes referred to as immunological memory because our immune system remembers previous enemies.

• Passive immunity - This type of immunity is “borrowed” from another source, but it does not last indefinitely. For instance, a baby receives antibodies from the mother through the placenta before birth and in breast milk following birth. This passive immunity protects the baby from some infections during the early years of their life