Mass vaccination centers are run on speed. In Oakland, California 6,000 shots per day were administered. In an 8 hour day, that is one shot every 5 seconds.
Do you think mistakes will be made? Who fills the syringes? Who gives the shots? Are they tired? Newly trained? At one every 5 seconds, who can check that they are all administered correctly? Do you really want to get injected with a new product when everyone involved in developing, producing and administering it has been going as fast as they can?
In Oakland, California it was discovered that over 3,000 recipients got the wrong dose.