Vaccinations work by introducing killed, weakened, or inactivated bacterial toxins into the body to sensitise the immune system.
These toxins stimulate a response from cells of the immune system called lymphocytes. There are around two trillion of these lymphocytes inside each of us.
When disease-causing toxins of the same type enter the body later on, the sensitised immune system rapidly produces antibodies to destroy them.
This animation looks at how vaccines immunise the body against potentially deadly diseases.
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Source: Al Jazeera