Registration and ethical approval
The trial was registered with the Iranian Registry of Clinical Trial (IRCT20140818018842N24). It was approved by the research ethics committee of the HORCSCT (IR.TUMS.HORCST.REC.1401.005) and the School of Public Health and Neuroscience Research Center-Shahid Beheshti the University of Medical Science (IR.SBMU.PHNS.REC.1401.112). The study was conducted following the principle of the Declaration of Helsinki and Good Clinical Practice. All study participants provided written informed consent for the vaccine booster dose, blood samples to be collected, and results to be published.