Randomisation and blinding
RECRUITMENT, BLIND
Participants were randomised 1:1 to IVIG or placebo treatment after consent was obtained. Randomisation was stratified by age group (< 1 year, 1–4 years, 5–9 years, 10–14 years and ≥15 years) and steroid treatment at the time of randomisation, using stratified block randomisation with randomly varying block sizes. Randomisation was performed using a secure web-based randomisation system (Sortition) which was developed by the Clinical Trials Unit in the Nuffield Department of Primary Care Health Sciences, University of Oxford.Participants, their parents or guardians, clinical staff and all study staff (including staff involved in recruitment, administration of study treatment, data collection and entry, and laboratory analyses) were blind to the treatment allocation through the entire study period. Study monitors who were independent of the study and all site pharmacists were unblinded to ensure dispensing of the correct allocation and robust IMP management at each study site. The placebo and IVIG were visually identical, due to the additional of 0.1% human albumin solution to 0.9% in the placebo.