Randomization and masking
PMBL
BLIND
The randomization list was generated by hospital pharmacy staff using Random Allocation Software version 2.0. Pharmacists also prepared identical packs containing 30 PMBL or placebo tablets each and labelled them with a unique code consistent with the randomization list. The individuals responsible for preparing the randomization list and tablet packs were not involved in the implementation of the study. Children attending the first visit and meeting all inclusion criteria and none of the exclusion criteria drew a card with a unique package number. Patients and investigators, including those responsible for immunoassays, were blind to allocation. Unblinding was performed after receiving patient diaries from all participants, that was in early November 2021.