Thread by @karamballes

🧵DCT trial results are being trumpeted by Telegraph today.

I was one of those saying they were unethical, and knowing how concerns of CEV families were treated in some of these schools I maintain that view.

I think its important to note the size and context of the trial.

Here's a link to the trial details.

The timing for the trial March to June was shortly after schools went back, cases were very low, Delta was still rising to dominance with cases starting to rise at the end.

https://twitter.com/BugsBernadette/status/1418438387766337538?s=19

I'm not an expert in this, but Jon is.

As he explains, the study is underpowered and contains gaps in the data, large margins of error, and inconclusive results

To claim this study is proof, is disingenuous

https://twitter.com/deeksj/status/1418474925090803714?s=19

This was when we had low Alpha transmission
47 control schools, 59 intervention schools had cases where DCT was relevant.

Note contacts identified by standard DfE guidence which we know is leaky (whole year groups aren't usually sent home from 1 case, particularly at this time)

Incidence was higher than index cases, thought this is due to not all schools actively reported cases and not all community diagnosed infections were reported or recorded.

The Orient LFD picked up 53% of PCR cases

We did not clearly demonstrate the superiority of the intervention.

"Despite the lack of statistical evidence" it should reduce absence rates but may be more limited

The margin of error for reducing transmission in this study is wide

Interesting that participation was lower in more disadvantaged areas, you'd think families less likely to be able to afford isolation would be keener to avoid it, could the higher liklihood of having an at risk family member have influenced this?

At some stages the interventions were paused because PH were concerned about Delta.

Can we apply a study done in low Alpha transmission to high Delta transmission?

Study has several limitations.
Did not directly measure in school transmission estimates based on community transmission
They did not estimate the impact of DCT in high incidence settings (as we have had now and will have in September)

Unclear if it can be generalised to other settings

They estimated in their calculations that having DCT increases weekly LFD from 30%-60%

Calculations assumed 1 positive case = 50 isolations

Does this study justify the headlines?

Why are PHE ppl and various ppl who keep saying transmission hasn't been an issue and schools and long covid is so rare we don't need to worry about measures crowing so much about this study?

I mean, the expert version of

"In your face people who thought not asking everyone involved for consent was unethical"

Seems a bit over the top when you read the study.

Worth noting only those who tested to skip isolation had to give consent.
I was told it was unfeasible for a school to get permission from all students...

My issues with the ethics and first hand account of how someone in a trial school was treated⬇️

https://twitter.com/karamballes/status/1393237625029398528?s=19

To be honest in a lot of ways its irrelevant because Gov aren't even going to bother with DCT in September, children no longer count as close contacts.

I suspect this will just end up being used to say schools are low risk (when infections are very low)

But it will be interesting how many ppl who hold up this study as solid enough evidence to support a policy will also say we don't have enough evidence/data on child vax or long covid to worry about a strategy that chooses mass infection over vaccination

https://twitter.com/karamballes/status/1417865527578578945?s=19

Another look at the study

https://twitter.com/dgurdasani1/status/1418531436286693384?s=19

What the results look like plotted

https://twitter.com/DGBassani/status/1418571952780894211?s=19