That’s tough.
And sometimes...quite often..alas advice from friends is ignored however it is couched. But on other hand in my experience very few friends resent the attempt to give advice unless it is phrased appallingly.
On that basis that it’s very unlikely to cause resentment and may do some good I think if I was “in your shoes”, I’d say “I’m really worried about you not getting vaccinated, would you consider talking about it with your doctor?”