For me it's been as simple as stating that normally vaccines are tested for years and years before being approved. This is done because the risks of long term health consequences is well understood and a real threat. These vaccines bypassed all long term testing. They have not been proven safe. Then throw the real numbers at them regarding adverse reactions and deaths. Then tell them the real numbers about COVID19. 2+2 = the virus isn't that scary and the vax is shockingly unproven.
It's all about the delivery but it works.