Vaccines are given to healthy persons BECAUSE

Mangoes get spoiled,not the jam made by them because

Vaccines are given to healthy persons in order to protect them from the risk of infection in future by same microbe. The vaccines are the attenuated (inactive) or heat killed microbes which mimic the disease causing microbe.  They do not harm the person but provide long lasting immunity against various infectious agents.
Jam does not get spoiled because it contains added preservatives and less moisture content which prevents it from spoilage.