I've had the same or similar conversation with some of my elderly relatives, but unfortunately there's no way to change their minds with logic or reason. It's a spiritual stronghold they're under (a "spell", brianwashing, etc.). You can't break a spell with logic or reason; you need divine intervention that can only come when the affected person wants it FROM THE HEART. This normally only comes after intense suffering.

OP -- you are not alone in feeling angry and frustrated and even frightened, but you have to let your mother be. You're only going to make things worse for her by harping at her. You've planted the seeds. It's up to her whether or not she wants to water them and let them grow.

When I was teenager, I did horrendously stupid things that my parents at first tried to prevent me from doing, like hitchhiking across the country. They told me about all the young female hitchhikers who were disappearing and ending up dead in garbage bags by the side of the road, but I didn't listen to their horror stories. It's not that I didn't believe them; I just didn't think it applied to me. I wanted to hitchhike across the country by myself, and nothing was going to stop me, regardless of how graphic the evidence was of the murdered girls. So, my parents eventually gave up trying to stop me from doing what they knew I was going to do anyway. They didn't agree with my hitchhiking plans, but they backed off and let me do my thing.

Needless to say, I had some horrible experiences that eventually brought an end to my hitchhiking days. But if I hadn't had those experiences myself, I would not have stopped hitchhiking.

What I'm trying to say here is that some people need to experience intense pain before they snap out of the spell. Until that happens, you have to let them make their own decisions, however wrong you think those decisions may be. You have to let them suffer the consequences of their choices.

Life's lessons can be very, very harsh sometimes, and it's just as hard for adult children wanting to protect their elderly parents as it is for parents wanting to protect their young children. There's always a point when the protective parties have to back off and let the mistakes be made.

Even so, there's a chance that your mother might change her mind. Something might intervene between now and when she's scheduled to get the shot. If you're a praying person, pray for her. I'll pray for her, too. When you invite God into the equation, he respects free will, but he sure knows how to persuade. And his timing is always perfect.