What is Vaccination?
[[File:Vaccination-polio-india.jpg|thumb|right|A child in [[India]] is being vaccinated against [[polio]].]] A '''vaccination''' is a treatment which makes the body stronger against an [[infection]]. The body fights infections using the [[immune system]], which is made up of millions upon millions of cells including [[T cells]] and [[B cells]]. An important part of the adaptive immune system is that it is much stronger when fighting a disease that it has already fought against before. Vaccination involves showing the immune system something which looks very similar to a particular [[virus]] or [[bacteria]], which helps the immune system be stronger when it is fighting against the real infection. The World Health Organisation estimates that vaccines save 4-5 million lives per year.<ref>{{Cite web|title=A Fresh Shot|url=https://policyexchange.org.uk/publication/a-fresh-shot/|access-date=2023-10-20|website=Policy Exchange|language=en}}</ref> ==Vaccination versus immunization== Another word used for [[vaccine]]s is [[immunization]]. These words mean things that are a little different. Vaccination is when a person is ''given'' something to make the immune system learn to fight an infectious disease. Immunization is when a person's immune system learns to fight an infection. Immunization can happen from vaccination. But immunization can also happen from getting the ''infection''. For example, a person can be immune to [[hepatitis B]] if he gets sick with hepatitis B. After a person gets hepatitis B and then gets well, he is immunized from getting it again. A person can also be immunized from hepatitis B by taking the hepatitis B vaccination. So vaccination and immunization have meanings that are a little different. But when people say these words, they usually mean the same thing. == Herd immunity == {{main|Herd immunity}} Herd immunity is an important part of how vaccines work. A herd is a group of animals. Herd immunity happens when most of the animals in a group are immune to an infection. If most animals a