They are probably zero in order for them to vaccinate this age group. Info is likely to be available from other countries. However people should not assume that this age group can't suffer the usual covid problems.
Some work has been done on why some people have a worse experience with covid than others. They know what can be wrong with people that causes people to suffer more but not the rest of people who do. No clear results as far as I am aware. Some at all age groups don't really notice catching it at all, some do to varying extents. Age effects are another factor. Some of that may be down to us only really evolving to live past 30 or so. Various changes have allowed us to live longer but that is the age where things start declining.
LOL I wonder if it's an evolutionary thing. Virus have always been around so some variation in peoples immune system and body makes sense to prevent the species being wiped out. Some always survive.

Or have so far.