He is remarkably stubborn in this area. It could hurt him with many voters as well. Though it isn't currently. At least if you believe in polls. It won't move the needle much for me because I don't believe he supports mandatory vaccines for covid. Could be wrong on that but I haven't heard him say that yet.
IMO, all he'd have to say is something like this.
"We were faced with a new virus that we didn't know much about. I pushed the agencies to work faster and harder than they've done ever before to develop a vaccine to protect the US citizens. I never mandated it or believed that it should be mandated in our country, or anywhere in the world.
As time has gone on, the effectiveness of the vaccines doesn't seem to be as high as what our administration was told by the drug companies and Dr. Fauci/Byrx. My hope is that the companies will be very transparent with their research that they had at the time, when they sold the government and the citizens on a "safe and effective" vaccine.