I suspect the study is not taking into consideration that the older and also those suffering from major health problems are much more likely to get vaccinated. They are aware of their frailties and are careful to take precautions.
Therefore, since those who are older and have health problems are the largest group to get vaccinated, ....the results of the study would show just that.
If you are old, infirm and suffering life threatening health problems, you are the most likely to die.
Thus another great discovery.
Not only that, the older get a ‘special vax’ that’s much stronger than the one given to everyone else.