Boris Johnson this morning told TV cameras the 'risk to teachers [of catching covid] is no greater than it is to anyone else'. Hancock made same claim.

The claim - which if true, would destroy a key argument against opening schools - seems to be based on this from SAGE (1/)

But there is a problem. That ONS analysis is based on data collected between 2 Sept and 16 Oct. For most of that period cases among school age children were similar to other age groups. More importantly, overall cases were very low (2/)

Now compare those ONS charts from Sept/Oct to the most recent ones. From 7 Nov to 18 December cases among school age children were consistently higher than everyone else. By end of term secondary school pupils were 3x more likely to be infected (3/)

It's not credible to suggest increased rates among students won't pass on to teachers. In fact, later in same SAGE doc Johnson/Gove are quoting they include results from Schools Infection Survey (SIS). In 105 schools they surveyed, rates among staff and students matched (4/)

And this could underestimate the problem for school staff. That's because SIS is biased to include only people without symptoms. As children are more likely to have asymptomatic covid, SIS study will be better at finding covid among students than their teachers (5/)

Thus if symptomatic cases were included, we'd likely find cases among staff to be higher than cases among students. That would mean if secondary school students 3x more likely to have covid than adults, teachers would have plus 3x more covid cases than non-teachers. (6/)

Of course there are lots of inferences being made here, and I'm sure enormous margins of error. But it's more credible than taking a study from before there was an epidemic in schools and presuming it will still apply now. That's what Johnson/Hancock are doing (7/)

Finally, whatever your view on school closures (FWIW I think clear they should all close) - I think we can all agree teachers deserve to be told truth about risks they face, and public should not be misled about risks teachers are asked to take on our behalf. (8/8)