1. Originally, the live vaccine (vaccinia, cowpox) virus inoculated in the skin as prophylaxis against smallpox and obtained from the skin of calves inoculated with seed virus. Usage has extended the meaning to include essentially any preparation intended for active immunologic prophylaxis; preparations of killed microbes of virulent strains or living microbes of attenuated (variant or mutant) strains; or microbial, fungal, plant, protozoal, or metazoan derivatives or products. Method of administration varies according to the vaccine, inoculation being the most common, but ingestion is preferred in some instances and nasal spray is used occasionally.
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