Randomisation and masking
Participants were randomly assigned (2:1) to either nOPV2 or placebo, using a block randomisation of size 6 or 12 generated by a statistician who was not otherwise involved in the study. The statistician prepared randomisation lists for study nurses or investigators who were masked to the allocation of the vaccine or placebo. Parents, investigators, and laboratory personnel responsible for the various analyses remained masked to group allocation until the end of the study.