Small pox vaccines can only be tested on humans, however Bc the flu can replicate in pigs, scientists can tests vaccines on pigs. Since there are two means in which it can spread, scientists must be aware of the genetic difference between humans and pigs and act accordingly. Influenza vaccines might have greater success rates Bc of their ability to test the efficiency of their vaccines on pigs in comparison to small pox vaccines which can only be tested on humans.
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