Excellent, more Sunday night T&T/public health announcements!

We all so want this kind of thing to be in place but please can we ensure nothing's rolled out before we actually know the results of the Liverpool trial.

And this still relies on so much else still being in place... https://twitter.com/hendopolis/status/1330633718399111170

Some immediate thoughts whist we await plans

Firstly - the plans suggest only rpt tested for one week.

The incubation period for COVID-19 is up to 14 days. And whilst median is 4-5 days, around 97% of cases become infectious withing 11-12 days.

That's still more than a week

Secondly, the tests mentioned are lateral flow tests. These have a specificity of about 99.7% and a sensitivity more like 76%.

Although sensitivity drops massively if you're not trained in taking the swab - it relies on the test being done properly. https://twitter.com/ScienceShared/status/1326563891766243329?s=20

In Liverpool, the army did mass testing. Mass testing at that scale isn't an option for most local authorities with current workforce and commitments, so this may mean people testing themselves at home if rolled out?

The subsequent lower sensitivity means more false negatives, but daily testing and the fact there's a higher sensitivity with higher viral load means this may not be so much of a problem.

Would need to see the trial data.

False positives are also an issue. Depending on how well we're doing at case finding and reaching contacts, this could *easily* be 150+ false positives in Eng a day.

Therefore, again need to be processes for either follow up PCR for those testing +ve, or rpt lateral flow tests.

But to know the true extent/impact of all this, will really need to see what happens in the trial in Liverpool - how it works real life.

More on positive predictive value/negative predictive value here: https://twitter.com/ADMBriggs/status/1326573271068909572?s=20

Thirdly, the real issue remains about how people behave.

Cases/contacts aren't isolating mainly because of not having enough support to do so. @SusanMichie (and her CORSAIR study) has been making this point for months

https://www.medrxiv.org/content/10.1101/2020.09.15.20191957v1 https://www.gov.uk/government/publications/spi-b-impact-of-financial-and-other-targeted-support-on-rates-of-self-isolation-or-quarantine-16-september-2020

And so it becomes equally important to understand people's behaviour if being identified as contact and asked to test themselves every day.

How do people get tests?
How long will it take from being exposed to the index case to getting tests?
Will people know how to use them if doing themselves?
What to do if you miss a test?
Will they tell people if it's positive?
Will they isolate if it's positive?

And Test and Trace will remain as important as ever.

All cases need to be reached to identify their contacts (currently around 85% are reached).

Those cases need to tell T&T about their contacts (about 80% of reached cases report having any close contacts)

And then all those contacts still need to be reached to be told to get daily tests. T&T is struggling to get to more than 60% of known contacts.

Plus it all takes time, shortening the time from +ve test to reaching contacts is crucial.

At what cost? Operation Moonshot was said to have a budget of £100bn and could that money have been better spent on isolation support/local government etc?

And finally, what is the impact of all this on inequalities?

I get the benefits of this could be huge in terms of work/families/school etc. But there are also huge unknowns and possible harms.

So again, @DHSCgovuk, *please* await (and publish) trial results before rolling out.