Thread by @chrischirp

THREAD on SCHOOLS:

It's now 4 weeks since Scotland & Wales started a phased return to primary schools (secondary schools went back last week) & 2 weeks since all schools in England went back.

What is happening? 1/15

First let's look at Wales. They started sending young kids back to nursery and primary schools 22nd Feb. Older primary school kids & secondary school went back last week.

Wales publish new Covid incidents in schools - and (unsurprisingly) incidents are increasing. 2/15

Secondly, Scotland. There we have case data by age.

Primary school kids only get a test if they get symptoms. School staff can get tested without symptoms if they want. All positive cases from lateral flow device tests (LFDs) are PCR confirmed.

Testing has stayed flat. 3/15

So changes in case numbers by age are unlikely to be due to more tests being taken.

What do we see? Cases in kids under 14 definitely going up. Cases in older kids & adults have stopped falling - and *maybe* - have started creeping up.

Most under 64 unvaccinated. 4/15

Absolute numbers are low still but also many kids under 14 who get Covid will not get symptoms (and so won't get tested).

It's *possible* (but uncertain) that flattening & recent increase in other age groups are cases spreading to older school ages (household tranmission). 5/15

Certainly in week to 13th March, ONS infection survey saw signs of overall increase in cases in Scotland. 6/15

Finally, England where we have much less data so far. Massive increase in LFD tests since schools went back, but about same number of tests early this week compared to week 8th March. 7/15

The *first* 3 tests by pupils were done in school and positive cases did NOT get confirmatory PCR tests.

But this *does* mean that case numbers are quite up to date since LFD results come through within an hour.

LFD cases have gone *up* this week compared to last week. 8/15

These positives are unconfirmed by PCR, but given roughly same number of LFD tests week on week, unlikely to be a false positive effect, but probably is more transmission - again not really surprising given that loads more kids mixing and not really any more mitigations! 9/15

Overall, numbers of LFD positives are low compared to number of tests though.

But hard to interpret positivity rates. Given that LFD tests are hard to do and given that we know they are not that sensitive, we are likely missing cases too. 10/15

From end of this week onwards, LFD testing for students and staff shifts to *home* and is entirely voluntary. We are likely to see fewer tests done *and* they will likely be done less well -> fewer cases detected (bad). 11/15

But home tests *do* get confirmatory PCR (good) leading to fewer false positives (good). So we expect to see a natural reduction in *reported* cases as testing shifts to home. So even if *actual* cases increase over next few weeks might be hard to spot in the data. 12/15

By the time you might see spread into symptomatic cases in older ages we'll be in the school Easter holidays where you expect cases in children to drop quite a bit as we saw in Oct half term and Dec holiday. So interpretating data over next month in England will be hard! 13/15

But overall, clear signs from Scotland & Wales that opening schools does come with increased cases in children. This is not surprising. But if they spread to older age groups (as might be happening in Scotland), then that can push R>1 - not good. 14/15

Slowdown in rolling out vax to <50s, to honour 2nd doses (important to do!), means it will be a few months before many school staff & parents will be protected.

Will this slow the roadmap? Depends very much on what happens next few weeks and how govt reacts to the data. 15/15

PS for avoidance of doubt, I think we should try to avoid cases in kids too! I don't want people to think that I think it's fine for lots of kids to get Covid.

PPS I'm told that there *is* more testing in school kids happening in Scotland that might explain some or all of increases in ages 0-14 but I can't find the data on it (might not be public). Also more people out & about in recent weeks.

Interpretation is tricky, not definitive.

PPPS Note that however cautious you are about interpreting Scottish or Welsh data, it's not great news for England where we opened schools all at once and with far fewer mitigations in place.