They will dismiss any and all medical arguments that you make. The CDC, FDA, and the mainstream media says it's safe and that's enough for them. They will look at you like a person who is trying to prove that the earth is flat and will interpret the evidence you present in that light, if they care to look at it at all, which is doubtful. HR knows the courts are siding with employers on this. HR's goals are twofold: One is to be risk-averse for the employer. And two is to push the leftist narrative--virtually all HR employees are the most rabid leftists. My suggestion is to get a copy of their vax policy in writing, which should explain religious and medical exemptions. If they don't have one then it's a good indication that they will deny your exemptions by making up rules as they go along. My other suggestion is to drag this out as long as possible. Make excuses for why you aren't vaxxed yet or say that you lost your vax card and can't get another one. Time will reveal approaches to the problem that you could not have foreseen.