Peston: Why the NHS coronavirus app won’t work well for long unless we find out if infection delivers immunity

Assume an alert flashes on your NHSX Covid-19 tracking app that you've been in contact with someone who has the virus.

This means that you and those you live with are supposed to self-quarantine for 14 days (not seven).

Now if you have symptoms, you would be allowed to have a test to ascertain whether you do in fact have the virus.

But you would not be allowed a test if you don't have the symptoms; you just have to sit at home and see if you develop symptoms.

So if you are unlucky enough to constantly be bumping into people with symptoms, you could find yourself in a new steady state of repeated 14-day household lockdowns.

Also, since we don't yet know whether having the virus confers immunity, right now you would have to go into 14-day quarantine, with your family and those in your home, even if you've already had the virus.

All of which means that testing, tracking, tracing and quarantine is only a sustainable approach to containing the virus over the long term if a reliable blood test is found for home testing to show whether we have Covid-19 antibodies - and those antibodies are proven to provide immunity to re-infection.

In the absence of knowing whether any of us are immune, we'd probably all go stir crazy from being repeatedly put into de facto house arrest, each time the app buzzes the warning that we've been near an infected person.

But don't despair too much. As I understand it Matt Hancock thinks in the coming weeks he may receive data from a survey (one that I have not yet been able to locate) that will tell the government whether antibodies deliver immunity.

Fingers crossed, on all counts.

PS I guess this is the Porton Down blood-based survey we'd all forgotten about. But I thought it was about prevalence of the virus, not immunity.