The activity of purified and unpurified virus. The chart graph shows the process of 50% cells exhibiting CPE as the infected time goes on according to the number of wells. The unpurified virus was used as a criterion to measure whether the purified virus was still active enough. As the infecting days went by, the number of wells appeared 50% CPE was increasing. The curvilinear trend of purified virus is in accordance with unpurified virus, and the wells exhibiting 50% CPE in purified virus per day is slightly less than that of unpurified virus.