So... a thread on coronavirus, testing, and the Govt's possible exit strategy. There are big logistical, behavioural, and ethical questions ahead. Would be very interested in others' thoughts... 1/11

We know that there are two sorts of tests. One which shows (at a snapshot time) whether you have the test. And one - said to be 'the real gamechanger' - on whether you *have had* the virus, and so are no longer susceptible. 2/11

The first is of some utility. It can help NHS staff and other key workers (eg who are self-isolating) to be able to return more quickly. It also helps - greatly - to develop understanding of the spread of the virus. 3/11

But - of course - those who don't have the virus today can contract it tomorrow - so the knowledge that you do not have the virus today, tells you nothing about whether you will contract it tomorrow. Lots of repeat tests need to be available; and - for now - they are not. 4/11

The antibody test - to identify that you have had a virus is very different. It provides a credible path to an exit strategy. Those who have had the virus are 'safe', and there is no scientific reason to keep them under lockdown. 5/11

As more and more people are tested, and shown to have had the virus, life can begin to return to normal. [At least, that is my understanding of the theory; do please correct me if I'm wrong...] 6/11

I fear that there are a few - rather difficult - problems ahead (if this is indeed the strategy). This is just a first think - and I'll start by identifying just two. I suspect that there are many more. 7/11

First, the accuracy of the test is crucial; as is the ability to test many millions of people. Is that scientifically, and logistically, possible? 8/11

And second, this strategy creates a sharp distinction (in society) between those who can show that they have had the virus, and those who cannot do so. This may be difficult to sustain, and may have unpredictable social effects. 9/11

It also - surely - creates a strong (perhaps overwhelming, social and/or economic) incentive to show that one has had the virus... and to do that, you have to catch the virus. Hmm. 10/11

In the absence of a vaccine, an exit strategy based on testing seems to be the Govt's (emerging - and perhaps best) 'strategy'. The message here is that it needs very careful thought. 11/11