I think schools will have had a reduced impact on numbers in the past week or so.
Years 11 & 3 had finished.
Private schools would have finished a week or 2 early anyhow.
And a huge number, maybe 10% or so of the rest were off school, either isolating or asked to work from home as part of the school's plan.
My hunch is that the 10% working at home, like my DC< would have been far far less likely to get infected.