Randomisation and masking
Participants were randomly assigned 1:1 to receive either a standard dose or a fractional dose (one-fifth the standard dose) of the 17D-213 YF vaccine lot 598 with a release potency of around 67 608 IU per dose. The potency of the vaccine was confirmed at the National Institute for Biological Standards and Control (Potters Bar, UK; Randomisation was done in non-disclosed variable block sizes of 6 or 8. The randomisation sequence was pre-generated and concealed in a scratch-off booklet by an independent firm (DiagnoSearch LifeSciences, Mumbai, India). Participants and study personnel following safety and immunological outcomes were blinded to the allocations throughout the study. The vaccines were prepared at the start of each vaccination day by the unblinded personnel (the vaccinating nurse and pharmacist) on the basis of manufacturer's instructions and were kept at 2–8°C until administration. Vaccines were administered subcutaneously. Standard doses were dispensed using 0·5 ml auto-disable syringes (standard subcutaneous needle size 25G × 3/4”) at about a 45° angle. Fractional doses were dispensed using 0·1 mL auto-dosing syringes (needle size 26G × 3/8”) at about a 90° angle to achieve subcutaneous delivery.