Being highly intelligent demonstrably does not prevent you from coming to unsound conclusions. My favourite example is Linus Pauling, who was a distinguished chemist that won Nobel Prizes for both Chemistry and Peace. But later in life, in the absence of clinical evidence, he convinced himself that high dose vitamin C helps against several diseases including cancer, and aggressively advocated its use. He was simply wrong about vitamin C.I know a couple of highly intelligent people who are not getting the vaccination.
I am pretty sure that any rational comparison of the short- and long-term risks of delaying vaccination would demonstrate that your friends came to the wrong conclusion too. But irrespective of risk, who knows what will happen to them in particular? They have presumably survived so far without too much harm, and might well get lucky. I just hope they don't pass Covid on to someone else who might not be so fortunate.