Vaccines contain weakened microorganisms which are able to cause disease but not upto very extreme level which can cause great harm to the body.
Since vaccines cause the disease they enable our bodies to release antibodies which fight with the disease causing microorganisms. Antibodies have a memory of diseases which occur once. So, due to vaccines antibodies get formed in our body for the respective disease and if in future we get infected by those disease antibodies present in our body due to vaccines attack the disease and we get a cure in short period of time.
In this way, vaccines protect us from very harmful effects of various diseases.
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