Just an idle thought..
Ask them what the side effects are of the 'vaccine' they are taking. If they say 'none' then simply ask them how many pharmaceutical products have ever had zero side-effects.
I think this might have a chance of disrupting the signal for common sense to kick in, maybe. Worth a shot?
I work as a scientist. My coworker, also a scientist, is triple vaxxed.
I got him to question his beliefs by letting him explain to me how you would test a medicine. He was correct in his explanation, including a control group and a placebo group.
Then I asked him what the placebo for a vaccine should be. Then I told him to look up what is actually used as a placebo.
He was surprised and learned something that day.
what is used as a placebo for a vaccine test?
Another vaccine. An existing meningitis vaccine was used as the "placebo" for the covid vaccines in at least one study.
https://www.thelancet.com/journals/lancet/article/PIIS0140-6736(20)31604-4/fulltext