@notevenat20
The statistic itself that half of secondary schools have had at least one case is really not remarkable. The average size of a secondary is about 900 so that could just mean 1 in 1800 children have it. That would be a very low number if true.
I am sure the true proportion is much higher than that but you can't guess it from the school stat.
Half of all schools have had at least 1 case in
one week.
If the children are packed together on buses and in corridors and classrooms, and they remain together in classrooms all day, then the chance of aerosol spread is very high.
Also,secondaries are closely interconnected through friendship, family and social groupings, so the risk of spread from school to school is high.
We know that 1 in 100 secondary school children is confirmed to have covid (see previous graph). Note the slope of the curve at the end.
However, with poor levels of testing & asymptomatic spread this could even be higher.
As you know, immunity does not appear to persist reliably, so this is not a good reason for wanting children to get infected.