 Interim Analysis: The treatment regimen chosen for Part 2 will be based on the analysis of Part 1 data. A detailed Statistical Analysis Plan SAP will be prepared for approval by the Sponsor prior to performing any unblinded analysis for presentation to personnel designated as being blinded to the randomization. A data safety monitoring board DSMB will conduct a blinded review of source verified safety data. If there are no safety concerns, an independent statistician will perform an unblinded futility analysis of preliminary efficacy data from the four cohorts; blinding to treatment group celgosivir or modipafant will be maintained, however placebo will be unblinded. If futility is concluded, the Sponsor may elect to discontinue the study. If a signal is detected, a sample size calculation will be undertaken for Part 2. The Sponsor will convene a Scientific Advisory Board SAB who will then review unblinded log10 serum viral load AUC for viraemia and platelet count data to recommend which dosing monotherapy dosing regimen to advance to Part 2. If the recommended sample size for Part 2 exceeds the maximum specified for Part 1 and 2 a total combined sample size of N 132 participants for a monotherapy, the Sponsor will submit a major amendment for Institutional Review Board Health Science Authority IRBHSA consideration prior to initiating Part 2. 