Limitations
DISEASES
We acknowledge the limitations of this study. First, up to 30% of volunteers with controlled underlying diseases were selected. This may have impacted the overall VE in this study. Second, we could not run serologic tests for all our participants at baseline due to our limited resources in Iran. Third, given that the older population had undergone mass vaccination during the study period, this age group underwent premature unblinding to receive approved vaccines, a procedure that could lead to selection bias due to the nonrandom exclusion of this group postrandomization; it was an ethical decision and was based on good clinical practice standards. Also, the magnitude of this bias was not considerable (approximately 2.5% of the total sample).