ID50 describes
A) the number of cells or virions needed to establish an infection in 50 percent of exposed hosts.
B) the amount of toxin lethal to a 50-pound human or other animal.
C) the number of cells or virions which will kill 50 individuals.
D) the number of cells or virions which will kill 50% of exposed hosts.
E) the percentage of individuals which will develop an infection after exposure to 50 cells or virions.
Answer: A
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