Randomization and masking
The block randomization method was used with block sizes of 2 and stratified by age group. Eligible participants in each cohort were randomly assigned at a 1:1 ratio to receive Ad5-nCoV or inactivated vaccine. Randomization was done using a sealed enveloped system integrated with the electronic case report forms in the Open Clinica platform. A random number was assigned to each participant by allocation of the next available randomized entry in the randomization list (generated by an independent statistician using SAS (version 9.4)) that was established before the start of the study.During the double-blind phase, the participants, investigators, and outcome assessors were blinded. The personnel who prepared and administered the vaccinations were not blinded, but they were not otherwise involved in other trial procedures or data collection and signed a confidentiality agreement. In addition, analyses of the safety and immunogenicity outcomes were carried out in a blinded manner by the lab technicians.