The situation may well change in September. We quite often have classes covered by SLT in the event of staff absences but have not been crossing bubbles at the moment. I was really only referring to this school year when school is not functioning normally. Ours would likely revert to being covered by SLT come September whereas other schools may take in supply staff because, as you say, shutting down classes due to staff absences is not sustainable in the long term . We have had no confirmed cases of Covid19 from staff or children to date. Although, there are a few members of staff who are convinced they had it before the first reported case in the UK!!