For double and triple combination studies, each drug was tested in triplicate at five or six concentrations (including no drug), in which the high concentration for each drug was set to approximate the EC 50 of the drug as a single agent. The concentrations of each drug used in double and triple combinations against each virus are provided in Table S1 . The cytotoxicity of the double and triple drug combinations were determined using the same experimental format in three separate experiments, and using the same concentration ranges as outlined in Table S1 .