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8.) "Herd Immunity" is achieved if a large enough percentage of the population contract the virus, letting their natural immunity develop antibodies, and thus making it difficult for the virus to further spread to the more vulnerable members of the population. It is estimated by some that if roughly 67% of the population contract a virus, herd immunity will be achieved. a. Using your hypothetical model from #7, estimate how long it would have taken the U.S. to reach herd immunity