Randomization
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The randomization sheets were generated by the trial statistician (James Watson).All new randomization sheets and all updates of existing randomization sheets were done using a prewritten R script which was stored on the randomization Dropbox folder owner is MORU, under custodianship of the head of MORU IT; this file is a full ‘Professional’ version with history recorded and only the trial statistician and head of IT had access. The file took the following inputs:Site codes (e.g., ‘th001’) for which to generate randomization sheets;The set of arms available for randomization in that site;The number of arm repeats per block (i.e., set to the minimum integer such that in each block there is an integer number for each arm);The randomization data file from each site (which has the patient numbers for subjects already randomized) named data-XXX.csv (where XXX is the site code), if this does not yet exist a blank csv (headers only) is generated.This R script is run every time a new site becomes active and every time the set of available arms changes. The output is a csv file named rand-XXX.csv (where XXX is the site code). This overwrites the preexisting file (which can be retrieved from the Dropbox version history). Each time the randomization script is run, this is recorded on a log file.The randomization is done according to the following constraints:Blocks of 2*number of available arms;Additional ‘fuzziness’ by swapping one patient allocation per block at random (this can be swapped for any of the available arms)—this avoids knowing which arm the last patient per block will receive.Each time an authorized member of the study team logs onto the web-app this is logged (timestamp and username).Each time a new patient is randomized this is logged on to the file data-XXX.csv (where XXX is the site code) with the following information:Subject numberScreening numberAgeSexMember of study team usernameTimestampAt the start of the trial (September 30, 2021), randomization to casirivimab/imdevimab was set at 10% (positive control), and the other arms had equal uniform randomization ratios of 22.5%. This was changed on October 30, 2021, so that all arms had equal randomization ratios. This explains why there are slightly fewer than expected patients randomized to casirivimab/imdevimab.