Moderna shares fell 16% on Aug. 20 after closing more than 170% higher the previous day, according to BIT (bit.com) market data. The earlier surge followed reports that a personalized mRNA cancer vaccine developed by Moderna and Merck had achieved major success in a phase 3 clinical trial involving high-risk melanoma. The report described it as the first mRNA cancer therapy globally to demonstrate efficacy in a large phase 3 trial.