In all my public schools, never were we given a shot.
In my entire elementary school "career", the only thing we ever did in school close to vaccinations was a TB test. A health department worker had the kids in a class walk by her in a line. She administered the test, and then handed out info sheets for parents. After the 2-3 day incubation period, the teacher walked around and checked the injections. If any showed potentially positive, those kids parents got a letter to have the kid tested again at the health department. If the kid was absent the day the tests were "read", they also got letters to have the test done again unless they had the test inspected by a healthcare professional the day it was supposed to be.
All actual immunizations were done at the county health department, a doctor's office, or the hospital. Schools would have required verified consent forms signed by parents to do in-school shots. Never happened.
Once the risk of adverse reactions was taken into account, in-school mass immunizations just made zero sense.
In the Air Force, I remember going to a large briefing for our division, and the shot clinic staff was there with flu shots. Each attendee had to stop at that table and receive the annual flu shot. That, even though we were already required to get a shot on our own -- which I rarely did. That has to be the only "mass" immunization I remember.
That doesn't count the people at the transportation center waiting to fly out to Saudi Arabia. Medical staff reviewed our shot records and gave us whatever we were lacking before departure. I seem to remember getting a tetanus shot once in line. Imagine the poor folks who showed up without their shot records. They were given everything required for the region we were heading to. I'm sure a 23 hour ride on a C-141 facing the rear of the plane was much different while also dealing with 4-5 vaccinations injected just before leaving.
In both cases, we were required to remain in the area for half an hour in case we needed medical assistance.