https://evidence.nejm.org/doi/full/10.1056/EVIDoa2300197
They just had two intervention groups. M received influenza vaccine messaging consisting of a video, one-page flyer, and scripted message. Q was even simpler and just asked "Would you accept the influenza vaccine in the emergency department today if your doctor asked you to get it?".
For people that don't often see the doctor outside of say hospital visits, it appears like simple outreach can do wonders for vaccine uptake. I wonder how effective such interventions at a dental clinic would be, given dentists can also be on the front line of early health interventions.