Limitation
CHRONIC DISEASES, BLINDNESS
First of all, the study was initially designed as an RCT, but due to the dissatisfaction of the volunteers with the blindness and randomness of the study, the study design was changed to a comprehensive cohort study. Second, the study did not include pregnant women or those younger than 18 years; thus, the efficacy and safety of the inactivated vaccines in these groups remain unknown. Third, the trial was mainly conducted on generally healthy Iranian people. There was insufficient power to test the efficacy among those with chronic diseases, older adults, and those in other geographic populations. Fourth, there were only two severe cases of Covid-19, so we cannot make conclusions about preventing severe cases.