The shame is for making a decision for a crap reason that's not logical.
The stated reason for not getting a booster today was "they're only 20 and 20 year old aren't at as much risk". That logic is only true if you're going to be 20 forever. Nobody on this thread has questioned that a 40 year old is at more risk than a 20 year old, and that a 60 year old is at even more risk.
So, using the reason of "not 40" or "not 60" as the reason to not get a booster or vaccinated today is a poorly thought out reason. And really, not getting the booster should mean you're deciding to not get vaccinated, since it's very clear that without you're not getting the full benefit of the vaccine.
All those 20 year old will one day be 40 or 60. They'll all be in the higher risk group then. Which brings us back, in the higher risk group they should all get vaccinated. Waiting now makes no sense at all. Plus, they all already made the decision to start getting the vaccine.
Unless you don't expect to ever get to the higher risk group. I don't know, maybe all those 20 year olds are daredevil stunt bike riders or base jumpers, or some other high risk group and they just assume they'll never get that old.
That's the point. It doesn't matter at all if the vaccine has a 1 year, 5 year, 10 year, 20 year, or longer efficacy. Whatever the answer is, eventually all us would like to end up in a group that is higher risk. If we're going to get there, it's an advantage to getting vaccinated and boosted now instead of waiting.
All waiting does is give you a chance to show up in a hospital asking the doctor if getting vaccinated or finally getting the booster now will help and getting to hear them say it's to late.